You've been lied to.
I'm sorry to be the bearer of such bad news, but you've been lied to. And it gets worse: you've been lied to by some of the people you admire and look up to, the most.
Specifically, you've been told that you should always give it your best. That you should always give 100%. Perhaps even 110%.
That is the path to success and excellence, is it not? That's how the rich and famous managed to climb to their position in life.
In reality, this is an idea that, if followed in earnest, will keep you small, weak and frustrated.