Just to reiterate, an idea that goes from 100% to 25% based solely on Paul Graham is not a good idea.
To restate the original point: I feel like some of the people on this forum approach starting a business the same way they approach applying to college, or to grad school. That is not how it works. Your success is not gated on the "grownups" in the admissions office, or the department, or Y Combinator, making a decision about you.
If you catch yourself thinking about it that way, stop. Even if you get your 2 month's consulting dollars out of Y Combinator, nothing else in business works that way. There's no professorship to apply to once you get funded. You actually have to engage the market and win.
I define "success" as being able to quit my day job and work on the startup full time. Anything after that is gravy.
My chances of being able to do that if I'm accepted to YC: 100%
My chances of being able to do that if I'm not accepted to YC: 25%
The 25% is more than enough to keep me going and to keep my inspired. But I'd still have a better shot if I got accepted by YC.