Any child who read maths textbooks with enthusiasm for 3-4 hours a day for years could in theory at least get close to doing what he did, but what kid had that level of motivation?
There is no way this is true. I've met and worked with enough people to know that not everyone has the same mental ability. There are some exceptionally sharp people and many dim witted ones too.

I don’t say everyone has the same mental ability. But I stand by my point. Those people you mentioned might be dimwitted in part _ because_ their lack of enthusiasm for learning is low, so they didn’t do it. I don’t care how smart you are, effort matters.

Yeah, Fermi was such an unmotivated slacker.

Relayed by Nick Metropolis: Fermi and von Neumann overlapped. They collaborated on problems of Taylor instabilities and they wrote a report. When Fermi went back to Chicago after that work he called in his very close collaborator, namely Herbert Anderson, a young Ph.D. student at Columbia, a collaboration that began from Fermi's very first days at Columbia and lasted up until the very last moment. Herb was an experimental physicist. (If you want to know about Fermi in great detail, you would do well to interview Herbert Anderson.) But, at any rate, when Fermi got back he called in Herb Anderson to his office and he said, "You know, Herb, how much faster I am in thinking than you are. That is how much faster von Neumann is compared to me." [0]

[0] https://news.ycombinator.com/item?id=39965802