I think the rags to riches story in Silicon Valley is highly exaggerated. For many entrepreneurs the first investment comes from family and friends, hard to do if you are from a poor background. Much easier to find investor and customers if you have connections who are well connected.
My own circumstances was an upper middle class background, however, my family was dysfunctional and non supportive, I left home at 19 and had to support myself including working my way through college. A big problem that goes with that is a lack of confidence which is required to sell yourself to investors, customers, and taking risk. Fortunately I cofounded a successful software company with outstanding people which not only made me well off, but more importantly helped me grow as a person.