I struggle with these tendencies too. For me, I think it usually stems from being interested in the product not the process--that is, if I could snap my fingers and immediately produce what it is I was envisioning (even though that initial vision is usually fuzzy) I'd do it.
I think people who can stick with things long-term enjoy the process of what they're doing at least on some level. What enables them to stick with something is not the goal post, but the activity itself. They're motivated to spend x hours a day building a roguelike not only because they're driven by the vision of what they're going to produce, but because they genuinely have tons of fun and get tons of satisfaction from the activity of writing a roguelike and solving the problems that arise in that domain.
Personally, I've found that this love and enjoyment of process is usually an acquired thing. It's just like going to the gym. Once you make it a habit it becomes easier and easier and you become so dependent on the rhythm and little boosts you get from going to the gym that your dream body or whatever initially got you in there pretty much becomes irrelevant—it morphs into an activity that's fundamental to your way of life, you need to do it, you become dependent on it.
I've found that sticking to intellectual pursuits long-term is analogous to going to the gym. If you force yourself to be consistent and to show up every day and commit some time toward your project, you'll soon come to love the process and it'll be much easier to see it through to the end.
It's incredibly hard but really important to resist the idea that you can bring your grand visions into fruition within a short span of time--it just doesn't happen, and it's these sorts of fantastic expectations that lead to eventual disinterest and burn out. If you're constantly chasing the finish line and fire up all cylinders to get there as fast as possible you'll never make it, but if you run for the joy of running and do so consistently you're guaranteed to get there eventually (the tortoise and the hare).
What you have described is just plain old discipline. I think the reason why side projects don't result in discipline is that they are just something you do when you have time for it. Work usually has a fixed schedule and any variable events are scheduled around work. Side projects tend to get disturbed by variable events and inevitably are delayed.
I think people who can stick with things long-term enjoy the process of what they're doing at least on some level. What enables them to stick with something is not the goal post, but the activity itself. They're motivated to spend x hours a day building a roguelike not only because they're driven by the vision of what they're going to produce, but because they genuinely have tons of fun and get tons of satisfaction from the activity of writing a roguelike and solving the problems that arise in that domain.
Personally, I've found that this love and enjoyment of process is usually an acquired thing. It's just like going to the gym. Once you make it a habit it becomes easier and easier and you become so dependent on the rhythm and little boosts you get from going to the gym that your dream body or whatever initially got you in there pretty much becomes irrelevant—it morphs into an activity that's fundamental to your way of life, you need to do it, you become dependent on it.
I've found that sticking to intellectual pursuits long-term is analogous to going to the gym. If you force yourself to be consistent and to show up every day and commit some time toward your project, you'll soon come to love the process and it'll be much easier to see it through to the end.
It's incredibly hard but really important to resist the idea that you can bring your grand visions into fruition within a short span of time--it just doesn't happen, and it's these sorts of fantastic expectations that lead to eventual disinterest and burn out. If you're constantly chasing the finish line and fire up all cylinders to get there as fast as possible you'll never make it, but if you run for the joy of running and do so consistently you're guaranteed to get there eventually (the tortoise and the hare).