It's not always or often about intelligence, it's about working hard and taking risks.
There is a great series on NPR called How I Built This. It's interviews of all these people that founded some of the most iconic companies in the US, only a few of them would be considered "very smart". Many of them talk about how they were average or poor students, but they did have a very very hard work ethic and they were willing to take risks.
Sure there a few of the people that are truly brilliant, a few that come from means. Those people would have been fine no matter what, maybe not billionaires but they would have been more than well off; but a majority were risk tolerant and very driven, hard workers.
https://www.npr.org/podcasts/510313/how-i-built-this