Actually I don't see how being a manager at bigco or being a wealthy student in an expensive school with lots of means helps you bootstrap a company on a shoest

Actually I don't see how being a manager at bigco or being a wealthy student in an expensive school with lots of means helps you bootstrap a company on a shoestring. I don't think the question is whether it helps you, the point is that it's a selection effect. Either the people who are smart and effective in those fields end up disproportionately wanting to go to big, brand-name schools and companies, those big brand-name schools and companies are able to hire those people, or both. It's possible that they also have a beneficial non-selection effect, but that's not what the parent comment was proposing.