One thing that having a kid taught me is that sleep deprivation really hurts my productivity as a programmer. It may be that some people can sleep 5 hours and function just fine, I'm not going to say everybody needs the same amount of sleep. But when it comes to work ridiculous hours I've yet to see someone regularly claiming 100 hours work weeks outperform me over any length of time.
If I can get in the zone and achieve peak productivity for 8 hours that is an extremely successful day. If I do that and then get 16 hours of exercise, healthy eating, and sleep then the next day I'll have made more progress in my unconscious and hit a positive feedback loop where elegant solutions to difficult problems present themselves effortlessly.
Contrast to my youth where I'd regularly "work" 12-16 hour days. Then I had the mentality that 5pm is a half-day, so if progress wasn't great by then I still had another 7 hours! This can lead to a negative feedback loop where you spend more hours trying to compensate for poor performance earlier.
I'm not claiming this as a universal truth, some people probably have greater capacity than me, but I know how easy it is to fool oneself.
>I'm not going to say everybody needs the same amount of sleep.
I am going to go one step further and claim that anyone who says they work 10+ hour days regularly and are still productive is full of shit. I have seen too many of those people either burn up or not actually be able to keep up with me when crunch time comes and a two day caffeine and less legal binge is the only way to do what you know needs to get done to ship.
What I have seen for people who supposedly work ridiculous hours is a largely useless body warming a chair and keeping middle management happy by being easily visible and "manageable".
My impression is that people who spend 10+ hour day in work tend to spend a lot of time socializing, on facebook or otherwise wasting.
The problem often is that their needs to socialize and relax are not lower. Without realizing it, they started to use time spend in work to fulfill those needs. It slows down everybody, but looks good to management.
For the sake of Yahoo I hope Marissa Mayer is just a liar because they might be still getting their moneys worth, even if she personally needs to feel like a hero by making claims about self sacrifice etc.
If she does what she says she does in terms of sleep, e.g. 130 hour weeks, then they are paying someone millions of dollars to make decisions in a state so impaired[1] that they would be better off just a random drunk bum on the street and asking him for his vision for Yahoo.
Everyone is not the same. I am definitely in the 8-hours-a-night camp, but a small percentage of the population seems to have a genetic variation that allows them to sleep much less.[1]
I'm Eastern European and when I was growing up I still had the cult of personality around Stalin in living memory. The sorts of claims they make about "short sleepers" there are exactly the kinds of claims that were made about Stalin and other high ranking Communists. This was the reason why they deserved to rule, just as these supposed short sleepers are the digital hyper capitalists who deserve to rule the world:
" Not only are their circadian rhythms different from most people, so are their moods (very upbeat) and their metabolism (they're thinner than average, even though sleep deprivation usually raises the risk of obesity). [...] "They encounter obstacles, they just pick themselves up and try again," [...]"Typically, at the end of a long, structured phone interview, they will admit that they've been texting and surfing the Internet and doing the crossword puzzle at the same time, all on less than six hours of sleep," says Dr. Jones. "There is some sort of psychological and physiological energy to them that we don't understand." "
Yet three years later there aren't any clinical studies that have followed these supermen for any prolonged period to see how they actually act in day to day life, just more self reports.
The dirty secret is drug use -- whether heavy caffeine or amphetamines. When we are young, pounding coffee or redbull is pretty much assumed necessary to get through a heavy credit load. Early 20s, stay up all night working and the body bounces back.
Start pushing 30 and in to middle age, these people are definitely using prescriptions drugs.
However, I find that I have a limit to the number of hours I can program a day, and a number of hours in meetings I can have in a day, but the two don't interfere with each other much so long as I'm taking care of myself.
I think a healthy sustainable mix for maintaining flow over the long haul is probably something like - 4-5 hours coding, 0-2 hours meeting/collaboration, 1-2 hours email, 2 hours reading/writing, 1 hour lunch
>>I am going to go one step further and claim that anyone who says they work 10+ hour days regularly and are still productive is full of shit.
I don't completely agree with that. People who achieve amazing things working even 16 hours a day are pretty common. I have done that many times in the past. When I did my engineering here in India. Preparing for public exams, and entrance exams- I have regularly worked on subjects like Math and Physics almost 15-17 hours a day. Most of friends who cracked the exams did the same. It happens all the time.
When I worked at the call center, I would show up at work at 1 AM in the night, get back to home by 11 AM, sleep till 4-5 PM in the afternoon and then work towards learning programming till 12 in the night again. I would do this thing every day, for months. Most Indian IT giants who get outsourced projects routinely over work their employees, I worked for one in the early part of my career.
But again its also about practice, and how much you can take. Most of it psychological. You can never do anything, you have convinced yourself that you can't do.
You will be surprised how long you can go sleepless, when that is the only option you have.
> I don't completely agree with that. People who achieve amazing things working even 16 hours a day are pretty common. I have done that many times in the past. When I did my engineering here in India. Preparing for public exams, and entrance exams- I have regularly worked on subjects like Math and Physics almost 15-17 hours a day. Most of friends who cracked the exams did the same. It happens all the time.
I disagree. I spent part of my high school in India and I have worked on Indian engineering entrance exams. They did involve extensive amount of working through problems. There was more memorizing rather than abstract problem solving. I am not convinced the amount of clear headed thinking that was needed to perform practice drills on problem sets is the same as I need when I need to design something new or write theoretical proofs.
Not that you can't go rage hard and convince yourself you can pull an all-nighter or whatever. I have only found that at the end of the day there are two results:
a) The stuff that you make is not up to spec.
b) You are tired the next day and your productivity is fucked.
> There was more memorizing rather than abstract problem solving.
FWIW, you need sleep for memorizing as well. Stuff just won't stick if you don't cement it with a good night's rest.
Cramming it all the night just before an exam does work though, I did that myself too, but I think it only worked because I already had a solid foundation. Also that will never work for "insight" type of questions, just rote memorization.
>When I did my engineering here in India. Preparing for public exams, and entrance exams- I have regularly worked on subjects like Math and Physics almost 15-17 hours a day.
And did you cut this down to (even) 10 hours and observe real changes in productivity?
>Most of it psychological.
No. You get physical symptoms from sleep depredation. You can't think these problems away but you can convince yourself you aren't having them. Doesn't actually change your body's need for sleep.
Sleep Loss Impairs Judgment, Especially About Sleep
Lack of sleep can affect our interpretation of events. This hurts our ability to make sound judgments because we may not assess situations accurately and act on them wisely.
Sleep-deprived people seem to be especially prone to poor judgment when it comes to assessing what lack of sleep is doing to them. In our increasingly fast-paced world, functioning on less sleep has become a kind of badge of honor. But sleep specialists say if you think you’re doing fine on less sleep, you’re probably wrong. And if you work in a profession where it’s important to be able to judge your level of functioning, this can be a big problem.
“Studies show that over time, people who are getting six hours of sleep, instead of seven or eight, begin to feel that they’ve adapted to that sleep deprivation -- they’ve gotten used to it,” Gehrman says. “But if you look at how they actually do on tests of mental alertness and performance, they continue to go downhill. So there’s a point in sleep deprivation when we lose touch with how impaired we are.”
Sleep plays a critical role in thinking and learning. Lack of sleep hurts these cognitive processes in many ways. First, it impairs attention, alertness, concentration, reasoning, and problem solving. This makes it more difficult to learn efficiently.
Second, during the night, various sleep cycles play a role in “consolidating” memories in the mind. If you don’t get enough sleep, you won’t be able to remember what you learned and experienced during the day.
>You will be surprised how long you can go sleepless, when that is the only option you have
Doesn't mean it's healthy. Doesn't mean that you are performing at max capacity.
Well said. I personally know someone who just recently qualified with a first in medicine. She claims that she achieved this by getting a good nights sleep every night (i.e. 9 hours). She claims that this is what enabled her to qualify to do medicine also. All her classmates in college did exactly what kamaal describes (I have done it myself). They worked all the hours they could get because they were so afraid they wouldn't make it. And they passed their exams. But they didn't get a first. She said she spoke to a few of them a few times saying how ineffective this was, that medicine is hard and to build up a mental map and solid understanding you need sleep. As a well slept person she could see how ineffective they were. But it takes discipline and confidence (and maybe a bit of devil may care) not to panic and most people don't seem to be able to do this in the face of what they think are very tough odds.
My own observation on programming (significantly less taxing than studying medicine - no matter how you slice it) is that you can do a few late nights but after that it becomes drastically ineffective and the people involved get more and more dunning kruger about it. In the end the whole "push" consists of almost entirely ego and bullshit and the code is appalling.
In my own experience, in the "short term" it really comes down to motivation / inspiration. If you are sufficiently motivated, overworking yourself seems to be far less painful, and productivity doesn't really seem to be impacted. I've certainly pulled all-nighters before with code going into production pretty successfully.
I specifically put short term in quotes because I'm not sure how I would define it. It probably depends on a lot of factors, but I wouldn't stretch it past several weeks. Way past that, motivation also seems to be highly impacted, and you become the kind of tired, error prone zombie who stretches out their 8 hours of work over 16.
Actually its about knowing when to sleep than sleeping less always, more like when to accelerate and when to brake. I guess that's what Edison did too.
Many times over a period what you really need is long stretches of un interrupted time to get something big done. You will have to take a break after that. Come back with a fresh purpose, an new challenge and start again.
> Most Indian IT giants who get outsourced projects routinely over work their employees
I've had to oversee a number of those for very large orgs and can vouch that the quality was consistently beyond terrible and caused no end of problems. Most of the work done that way was eventually thrown away.
> I am going to go one step further and claim that anyone who says they work 10+ hour days regularly and are still productive is full of shit.
It depends on the type of work, work environment, and people one's working with.
One environment I've worked in had almost nothing but 'performance budget' and 'risk budget' defined. It was fascinating for myself, a 20-something at the time, to sit in a quite comfortable office for 12 hour stretches just looking at numbers and figuring out interesting things to do. Invigorating, in fact, with almost no pressure, just fun.
In another I ended up in quite a large organisation as regional 'service delivery head' which basically meant fielding several hundred emails per day across quite a broad timezone. Despite a an array of systems hacked together across several decades, and perhaps that was the fun, the team and I were pretty productive, however defined, and cut operating expenses by a considerable margin. Less blue-sky, more operations focused, but fun long hours nonetheless.
Having a child was quite a learning experience: we're all learning, all of the time, and we're also doing stuff, all of the time. I now work for myself, and view time on HN, or watching recordings of STTNG, or walking in a local park, or going to local university art displays, very legitimately as productive time, as I'm exposed to others' views, findings, methods, and inspirations of people that create something great.
I can work 10 hours a day and be quite productive. I don’t do it on a regular basis but when things get tough I can keep a schedule like that for weeks. Difference is though that I work from home. So I don’t spend time on various trivialities and I split my 10-hour work in two parts with a nice two hour nap in between. Also I’m an early riser. Starting my day at 5:30, by midday I've accumulated 6 hours of very productive work. I won't argue that working long hours is the smartest thing anyone can do but it's nice to know an effective way to do it if the need arises.
> If I can get in the zone and achieve peak productivity for 8 hours that is an extremely successful day.
The reason going to office takes more than 8 hours of productive work is because in an office environment, there is other stuff to do. Go to lunch with co-workers, attend meetings, help someone on something minor. These are things that take some percentage of your time and that adds up. For example, a few weeks back I was working from Austin. I was insanely productive because I could spend long stretches of time quietly thinking and producing.
"Sleep Drives Metabolite Clearance from the Adult Brain
The conservation of sleep across all animal species suggests that sleep serves a vital function. We here report that sleep has a critical function in ensuring metabolic homeostasis ... the restorative function of sleep may be a consequence of the enhanced removal of potentially neurotoxic waste products that accumulate in the awake central nervous system."
TL;DR: sleep is necessary, otherwise it probably wouldn't have evolved in so many different species. If you're really lucky (and a dolphin), you can get by with only sleeping one hemisphere of your brain at a time: http://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep
Somewhere in the middle he describes experiments they made with sleep. Essentially, they took a person, made them sleep a lot and then measured performance difference. Performance went up.
Sleep a lot meant sleep enough to recover from sleep dept and then around 8 hours every night.
I once worked with a guy who only ever slept about 4 hours a night for years. He would then run a full marathon into work every morning. I can tell you right now, his body was there but his ability to do anything other than make small tactical decisions was destroyed. Having a strategic meeting about the direction of the company was pointless, as you could nearly see has brain unable to compute and think at that level. The end of the story was that he died on Mount Everest and the company has basically collapsed because of his poor management and some other financial irregularities.
> Over time, children’s books and magazines began to promote this type of Edisonian asceticism.
I remember reading a children's book on goblins. The theme was that these goblins worked late nights and helped humans with their chores while the humans snored and slept.
The book was actually a prize given to me in grade one for something that I did well in pre-school. Since it was a prize, the book was especially dear to me and I would read it over and over.
Now that I think about it, I have always been a "sleep deprived" person since childhood. I wonder how much of my life was shaped by that single book!
Losing sleep to hit a deadline the next day is valid, but it isn't a productivity enhancer. I have always needed a full 8hrs for good work. -- John Carmack
I have relatively poor attention span, and have trouble maintaining good sleep patterns. What I've found is that there is a sort of "Ballmer Peak" ( http://xkcd.com/323/ ) when I'm slightly under-slept where I can focus far better than when I'm fully rested. Of course it is a narrow zone and not really sustainable.
I wonder if that is the general experience in our attention deficient generation, and if that might be a contributing factor in people preferring to cut their sleep.
The cult of sleep deprivation is definitely the norm in the startup world. People seem to be proud to not sleep much. Makes me question how sustainable it is
Over the years I've found that I definitely need 8 hours sleep but didn't often get it. I would normally manage about 6-7 hours and would soon build up a deficit. This had a definite impact on my well being and performance at work. Recently I've started using a timer instead of an alarm clock to ensure that I always get eight hours. If I go to bed later I get up later. On the rare occasions that I go to bed substantially later (e.g. attending a concert) and so can't allow eight hours, I still cope well because I'm already well rested. Ditto for when my young son wakes in the night - previously this would have killed me.
I know this isn't viable for everyone but my employer allows flexible working hours.
The whole deficit thing is interesting. I've felt that I do that too, but I've also heard people say that sleep doesn't work that way. It definitely could just be that any time I'm sleeping more than 8 hours I'm just being lazy.
I don't think it's a zero sum game and I'm pretty sure other factors are involved e.g. stress, alcohol intake, volume of exercise, etc). I do know that my perceived quality of life is improved when I'm getting plenty of sleep, and for me that requires about eight hours.
As I wrote in my initial comment the occasional disturbed night is not a big problem when I'm well rested. Under those circumstances I never feel the need to get extra sleep to compensate for the lost hours.
I think it's a deficit in the sense it starts to sum up for a few weeks and you get progressively tired until it starts to harm you, your brain, whatever. You can revert your tiredness sleeping well for a few days but the damage caused by prolonged periods with insufficient sleep it's done and maybe can't be undone.
I have found to stay maximally productive and creative I have to switch it up.
If I just get in a routine it seems like things flag. The best thing for me is to laze off and sleep for 10 hours a day... casually poke around at some stuff for awhile. Then, have a burst of output and sleep 5 hours for a couple/few nights while spending the remainder in a flurry of concentrated activity. Then, back to a regular normal routine for a stretch. If I try any one of these for long it seems my productivity and interest flag though.
I don't know if it's just me or if we evolved to have periods of rest and stress.
There's an easy counter example: weightlifting. By taking Edison's example as a maxim he'd have all people interested in weightlifting spend day and night at the gym and hardly resting. I suppose he'd recommend you take 2-3 minute catnaps between sets to recover.
I think it would be more Edison would have you work to your output in the gym, and then move onto doing independent research on weightlifting during recovery times.
If you believe you can work equally good with sleep deprivation you should test it.
Start measuring how productive you are hour after hour, WRITING down(very important) not only how much you do but also your energy level. Do this for 40 days.
Now, for 40 days do the same but sleeping what you need, no timer clock.
Compare the results.
When I did it for a completely unrelated reason, the results were so shocking to me. I actually believed that sacrifice meant better results. It does not have to.
Probably you don't need to sleep much if your job does not require much from you, just meeting people, staying there and so on.
I do triple or quadruple my productivity. I do program machines, and those things make work for me, but what they do has to be perfect.
Remember Chernobyl or the Air France disasters. The mostly trained and smart persons become stupid after sleep deprivation.
I worked in small startups for many years, and then later I worked in big companies for a few years. From my own experience, I would say sleep deprivation has no point in a big company. It only makes sense in a small startup when you are trying to hit some very specific and life-altering deadline, such as a meeting with a potential investor, whose money might determine the fate of the company.
I recall a long stretch from 2003 to 2006 (myself and my friends were doing our own startup) where we were often working crazy hours to meet deadlines. I recall at one point a guy was going to come in and possibly invest half a million dollars -- that would have changed everything for us. I recall I worked for 20 hours, then I slept for 2 hours, and then I worked for another 20 hours, just so we could have a bug-free demo when the guy showed up. I recall another time when we had to meet with a potential investor at 12 PM on Thursday, and I started work at 11 AM on Wednesday, and I kept working, and I kept finding bugs, and I worked through the night fixing everything, and I worked right up until the meeting. Then the meeting ended at 1 PM -- I had worked 26 straight hours.
Sleep deprivation only makes sense in the life of the startup because that part of your life that you spend in a startup is suppose to be finite. Paul Graham covers this in his essay "How to make wealth":
"Economically, you can think of a startup as a way to compress your whole working life into a few years. Instead of working at a low intensity for forty years, you work as hard as you possibly can for four. This pays especially well in technology, where you earn a premium for working fast."
Sleep deprivation will always be a part of startup life -- that is natural. You face deadlines that determine whether the company will continue to exist.
In a big company, sleep deprivation doesn't make sense. I made this mistake when I first moved to big companies, and it took me awhile to unlearn the habits that I had acquired at startups. In a big company, your individual contribution is no longer a large part of of what makes the company go (you can shape the destiny of a company with 4 people, but not one that has 400 people). And in a big company, there are no particular deadlines that truly determine the fate of the company -- nothing that has the same urgency as "We are running out of money so we need tomorrow's potential investor to invest".
In a big company, in the future, I will be cautious about working an 80 week. But if I do a startup again, I know what I am signing up for.
I have maybe 6 good hours in any day which I jealously guard for programming, the other 2 is side work (no brain required for a lot of it), emails, financial stuff, general office work.
Something that took me an embarrassingly long time to figure out is that I don't need 8 hours sleep every night, just on average. The correct sleeping time turns out to be half the time I was previously awake for.
Four billion years of evolution? Professor Russell Foster from Oxford University has no clue, evoluton learned us to sleep polyphasic, like babies, where you need far less sleep than the 8 recommended hours. I'm sure even Thomas Edison took regular naps.
Calling Professor Russell Foster having no clue was a little bit harsh, sorry about that.
I wanted to point out that a biphasic sleep pattern (which is also a polyphasic sleep-pattern) is the natural way to sleep.
Due to the segmented sleep (at least 90 minutes between sleeps) the body produces prolactin, which makes the first sleep have more SWS and the second sleep more REM, therefore you sleep more efficiently and get along with less sleep:
http://www.ncbi.nlm.nih.gov/pubmed/9709935
On the one hand, I think you're probably right. I've had good experiences with implementing unorthodox sleeping habits.
On the other hand, I think we as a species have proven ourselves to be remarkably good at adapting ourselves to different circumstances, and 8 hours also seems to be a working approach, as well as one siesta during the day.
The biggest problems I faced with polyphasic sleep was that 1) the world assumes 8 hours nightly, so it was hard to maintain after being a student, even as a freelancer, and 2) it required more conscious effort than 'normal' sleep to maintain, partly because of 1. It often resulted in me getting too little sleep in the end, because life would throw a wrench in the schedule...
Still, it's utterly fascinating. In case you haven't read them yet, the blog posts by Steve Pavlina on his experiences implementing polyphasic sleep are quite fascinating (much as I'm pretty sure I don't like the guy, to put it mildly).
The argument is made that evolution is based on a light-dark cycle, but is also based on predators who prefer to catch prey asleep. Survival favored those who could awaken and stay awake until a threat has passed or until sustenance was secure. Sleep is often a luxury, and not due to unhealthy life always. And often we are entranced by what we are doing, living our dreams. Sleep is personal and largely subjective, there is no universal truth on it as long as we all have different lives.
> but is also based on predators who prefer to catch prey asleep
While it's true, that's why most people in ye olde times would awake about 1 am (gone to bed at 8 pm) have a snack and go back to bed.
Additionally there was also after snack siesta (we had those on Sunday afternoon).
In primeval times, having a brief pause relaxing in the tree after lunch seems like good way to prime you for sleep later in the evenings.
Sleep isn't a luxury, it's a necessity, necessary for our brains to defrag. Saying sleep is luxury is like saying eating isn't a necessity for survival.
As someone that at one point did trade day and night, I can tell you I was plagued by heart palpatations and general feeling of unease even after switching to 8hrs of sleep during day.
We aren't horses or cows, which do exactly as you say and nearly never sleep.
Our species has evolved for at least 50 million years to sleep on tree tops in nests for the full night within a colony, viz all higher primates and many lesser ones all the way down to Lemurs. The homo genus, where we have evidence, has shown exactly the same patterns of sleep as modern humans. And add to that the last 400,000 after the invention of fire where any modern camper wouldn't have felt out of place inside any group of proto-humans.
But then human ancestors probably didn't have to worry about predators at night so much, cause they could protect themselves and their dwellings with weapons, or live in trees, or co-operate to watch by turns.
Sleep is not a luxury; it is an absolute necessity for our mammalian brains to function properly. It is a stretch to call it subjective. While it may be loosely thought of as subjective in the sense that we are capable of staying awake for varying periods of time, it is not something that we are capable of healthily carrying on without. The times of day/night that we need to sleep are pretty consistently and inherently set in our brain, and the amount that is optimal has been extensively studied.
The simple fact is that our brain does a lot of work throughout a day, and, in its standard operation, waste materials build up that, in large enough quantities, cause dysfunction or, when pushed to extremes, damage of the brain. During sleep, the space around our neurons and glial cells expands, and, as I understand it, the postulated function of this is to permit better flow of cerebrospinal fluid through our brains and thus flush them of waste material. I had mammalian sleep explained to me this way by an Anatomy and Physiology teacher - quite simply, sleep is not something that our brains can go without, and a properly functional brain (that is properly producing melatonin) sets and enforces a pretty strict circadian rhythm wherein we are awake during the day and asleep during the night. That is not to say that we are not capable of flexibility in this regard, but pushing our limits in regards to sleep is not a healthy practice.
Natural selection tends towards favoring the individuals in a population that display traits that make them superior survivors and reproducers within the population's environment - while you say that it would tend towards individuals who were capable of maintaining proper function without sleep, I would argue that sleep is a sort of built-in necessity of our complex and highly developed brains and that proper function of our brains can not be maintained without it. I would hypothesize that any individuals that were born with genetic traits that incapacitated or limited their ability to sleep (i.e., genetically induced insomnia) would be at a pretty extreme disadvantage compared to other members in the population. Although there are many nocturnal predators, none have been enough of a threat to our species that it has limited us in any significant or tangible way, and nor have any of them become so well adapted that they regularly threaten or prey upon us while we sleep.
Natural selection does not do much in the way of acting on neutral traits - neutral genetic traits tend to remain relatively consistent in a population as long as the environment remains relatively consistent such that, relative to the environment, those traits do not become particularly advantageous or disadvantageous. While there are exceptions wherein extremes are favored, it seems clear that any disadvantages posed by sleeping at night (in regards both to our modern species and our ancestors) are far outweighed by the advantages of being fully alert and functioning during our regular operational hours.
As far as I can tell, some of us have ancestors who spent thousands of years above the Arctic circle, where the sun doesn't even go down every day anyway.
And there never were any other primates, or trees either.
In a lab based on extreme experimentation, there is no substitute for perseverance until a breakthrough is
achieved.
Even if you don't start out trying to emulate Edison, you end up that way.
In chemical research you don't just turn off the terminal when it gets dark outside and call it a day.
I never thought it was the least bit unusual that every grad student's lab had a cot near the desk. You really aren't going to get anything monumental done if you go home from work every single day.
What happens if you have a 36-hour experiment that must be carried to completion, or a client's chemical tanker at the dock for a brief 36-hour stay where they are loading or discharging products that no one else can handle either?
You wait a whole month for your ship to come in, what are you going to do, be too tired to finish the job?
What hurts your productivity more is the chemical toxicity much more than sleep irregularity.
In the industrial chemical world, there is more effort to avoid exposure the more toxic a material is, so it ends up being those things which are intentionally ingested that compromise performance.
Caffeine, alcohol, tobacco, and drugs are going to make you much more tired than you would be without them.
If I can get in the zone and achieve peak productivity for 8 hours that is an extremely successful day. If I do that and then get 16 hours of exercise, healthy eating, and sleep then the next day I'll have made more progress in my unconscious and hit a positive feedback loop where elegant solutions to difficult problems present themselves effortlessly.
Contrast to my youth where I'd regularly "work" 12-16 hour days. Then I had the mentality that 5pm is a half-day, so if progress wasn't great by then I still had another 7 hours! This can lead to a negative feedback loop where you spend more hours trying to compensate for poor performance earlier.
I'm not claiming this as a universal truth, some people probably have greater capacity than me, but I know how easy it is to fool oneself.