There are a few examples of startup founders who were potentially homeless if it failed (AirBnB is the obvious one...they started it because they were literally a month away from being homeless), but you're right, this is the exception rather than the rule.

I think what's frequently overlooked in the "how do I get the resources to found a startup without risking everything?" is that you don't do it in one shot. If you have zero in the bank, your first priority should be to get six months of living expenses in the bank, and that usually means taking a job and saving 25% of your paycheck for two years. Then once you have six months in the bank, your next priority should be to get 3 years of savings in the bank, and that usually means taking a better job and saving 50% of your paycheck for 3 years. Only once you've got about 3 years saved up are you really in a position to found a startup without having run across seed funding from an angel.

Few people really understand compound interest or how it works out in practice. It's not just about putting money in a bank account or index fund and letting it grow. It's about having successively larger cash cushions so you can take bigger risks with better risk/reward trade-offs.