This is a good analogy, but it misses the very important bonus that a profitable doughnut vendor is also in a good place to fund the development of the uber-nut.
This part of the argument feels strange to me. The average self employed person works more hours and makes less money than their employed counterparts. Building a business that covers a mortgage is one thing. Building one that throws off enough cash and spare time to disrupt an industry seems like an order of magnitude harder. As PG said in the one of the other threads-- empirically, we just don't see this happening very much at all.
