"There is nothing more damaging to a young man's character than for him to discover that he is clever."

I stumbled upon this once long ago and have not been able to (re)discover the source since. In my memory, it was attributed to Leo Tolstoy (or may have been a comment made by one character in reference to another in one of Tolstoy's novels). Or maybe I made the whole thing up and was simply chastising myself while trying to learn Russian by being clever instead of diligent.

It near perfectly distills so much.

I would prefer diligence over cleverness every single time, most especially within myself.