You have to be good, and also care, which is like effort. a lot of young people care or put effort into playing sports but most do not have the talent to make a living at it.

"Average intelligence and persistence has accomplished much more than genius"

For hard problems, high IQ is necessary but still insufficient. You are not going to solve a hard math problem with average IQ no matter how much persistence you throw at it.

> You are not going to solve a hard math problem with average IQ no matter how much persistence you throw at it.

I'm inclined to disagree, but there's an important piece here that I've found when solving problems that were at least hard for me: sometimes I can get hung up on making a particular approach work when it's not going to and what I need to do is back up and find a different angle of attack.

For example if you're solving a hard math problem with little math knowledge and average IQ, if you're really passionate and persistent about it, then you'd realize you first need to learn more math to build your understanding of the domain. IQ/persistence in this case is not really about the problem itself, but more about the problem-solving process itself.