I'm fairly sure this is a pretty important point.
If your belief was still way up above your ability you see yourself with less room for improvement; possibly justify slacking off and reducing your input because you already "know it all".
Keeping yourself of the opinion that you are "pretty good" but around 25% off of "the ceiling" or so means you can still see plenty space for growth and push for it.
The more you can do, the further you know you still can go, or something along those lines.
Just musing a related idea.
Yes. Having an awareness of something larger than you...keeps you hungry and self aware of your vulnerability. Which usually breathes....... effort.