The people most confident in their competence tend to be the least competent in practice.
The Dunning–Kruger effect.
Self-cheerleaders tend to be morons, the most intelligent people by their nature tend to second guess their own abilities. Idiots just stroll through life taking whatever credit they can grab.
“The only thing I know is that I know nothing, and i am no quite sure that i know that.”
-Socrates
"Throughout my life, my two greatest assets have been mental stability and being, like, really smart.’
-Donald Trump
See the difference? By genuinely doubting, aka examining your abilities, you are in more competent company.