I think there is a big gap in how different people see this. You are right, it is possible to survive. It is also possible to fail. For some people, that is fine -- they can call up an uncle, or a friend (Thiel) and land another job quickly that pays good medical benefits.
For others, an 20/80, or even 50/50 or 80/20 survive/fail just does not cut it. Perhaps they have crushing student loans. Perhaps they have no parents to fall back upon if things go south. Perhaps they have visa issues. Perhaps they have a sick parent to take care of (my case.)
I admire your ambition (and envy it.) I hope people who have social safety nets realize it though. Because not everyone does.
It reminds me of a fellow undergraduate Senior who looked down upon me for going to work on Wall Street while he did the more pure thing of going for the Peace Corps. I asked -- so how do you land a job when you're done with the 2yrs commitment? He said his uncle was going to hook him up at a hedge fund. Nice, if you can swing that. Me? I have no uncles at hedge funds, so the on-campus recruiting super-day was my one and only shot. I dont think that makes my choice less pure, it is just one of relative necessity.