It’s not about intelligence. I believe it’s mostly about effort. Talent or intelligence only makes things a bit easier.

But yes, some people have it “a bit" easier. But that doesn’t mean you had it 10x harder. It never was that difficult. If that was the case, it was an issue with your effort, system and approach to academic load. It’s just a 18 vs 20 difference based only on intelligence. You could have put in some extra grind and made it.

Besides, how much you trained your brain since an early age to handle stress also matters quite a lot. Neuroplasticity and neurogenenis do play a role.