Most highly productive people often worry they're not good enough--That's part of what drives them to keep striving. From George Washington to Abraham Lincoln to most of the many highly accomplished people I know, they're all driven by moderate insecurity and feelings of unworthiness. I hypothesize that lower achievers are too unintelligent or defended to feel that worry, that insecurity.
I believe that self-esteem programs do more harm than good. Enduring self-esteem comes only from ongoing accomplishment, not by virtue of being human, of a particular background, etc.
When I write and speak, in my professional as well as personal life, I often worry if it's good enough. More broadly, I worry whether, en toto, my life's contributions are valuable enough. I'm not worried into anxiety or depression but just enough that the worry, borne of only moderate self-confidence, does help me be my best self.