Self criticism is a double edged sword in that not enough may lead to unrealistic self appraisal, but too much could thwart your creativity and confidence.

Personally, I strive to improve on something everyday knowing I am not the best, but certainly, more than adequate. The rest takes care of itself.

Believe in yourself musically ! Have faith in your abilities on stage!
Without a humble but reasonable confidence in your own powers you cannot be successful or happy.