Contentment And Resentment

Why is that every time I start feeling that I'm working hard enough and not a complete idiot, and lull my self into a ( false ) sense of security; someone has to come along and reaffirm my only slightly weakened belief that I'm useless, incompetent and a fool who doesn’t put in enough effort?

I don't want to be the best at everything. But I don't want to be constantly reminded of my shortcomings. I just want to be content being who I am.