Confucius says

Book 14, verse 30
"One does not worry about the fact that other people do not appreciate one. One worries about the fact that one is incapable."

incapable....yeah...one always has to worry that one is incapable

Book 9, verse 11
"Yan Hui, sighing heavily, said: "The more I look up to it, the higher it is; the more I penetrate it, the harder it becomes; I see it ahead of me and suddenly it is behind....If I wanted to stop, I could not; and when I have exhausted all my talents, it seems as if there is something which he has established profoundly, but even though I long to pursue it, I have no way of doing so at all."

I feel this way sometimes about a lot of things/people....