I assume you're on the upper end of the bell curve. Well, unless you're the furthest to the right (in some combination of talents), then there's someone further out there than you. You can beat yourself up about not being as smart as they are, but you'd have to be the smartest to avoid it. So, maybe you should stop expecting that you should be able to keep up.

What's more, for some of these people, it wasn't easy for them, either. General relativity wasn't easy for Einstein. He literally asked someone to "come help me with the mathematics before I go mad". That is, Einstein thought he wasn't smart enough to understand it!

Comparing yourself to others on smarts is a game you can only lose, because someone else is always smarter. Even if you're the smartest (Einstein, maybe), there's some related area or different combination where you're not. Someone else is better at math... or has more background in algebraic topology... or Hilbert spaces... or...

So don't be so hard on yourself. Stop playing the comparison game, because you can only lose. Instead, be who you are, and make the most you can of who that is.