There are four groupings of a person's ability: stupid, smart, brilliant, and genius, and the differences between them are as follows:
Stupid: has little ability and doesn't work. Result: nothing
Smart: has little ability, but works hard. Result: great things
Brilliant: has lots of ability, but doesn't work Result: nothing
Genius: has lots of ability and works hard Result: great things.
As you can see, in the final analysis it doesn't matter how "intelligent" a person is; the only thing that matters is what you do with what you have. Even if you have all the ability in the world, if you don't work then you will accomplish nothing and you may as well have been born an idiot, for that is how history will remember you. If, on the other hand, you have average ability/intelligence, work hard and accomplish great things, then history will look at you and say "Wow that person did great things. He/she must have been a genius."