Don't party, don't have fun, make lots of sacrifices. Most people are not prepared to do this 1 thing.
Now being a billionaire is a very different story of course.
- Fallback scenario. Wordt case they can go home, or they have a heritage at one point.
- Environment. Probably a more stable environment / background.
- Network. Network to customers, capital, pr.
- Access to capital. Easier today.
Especially the fallback scenario is almost always overlooked. Most people who claim to have risked it all and were "living on the streets", always had some fallback in forms of well off parents (or simply stable parents).
It's just like the starving artist syndrome, where most of these "starving artists" actually have a huge fallback, but they simply don't want to use it. But just by being there it helps a lot.
Free climbing is a lot different than climbing with ropes. Even if you didn't need to use them.
Most successful Phillips Exeter graduate doesn't quite have that ring for the Horatio Alger idea that is being pushed.