This is a great quote:

“Taking an honest inventory of our musicianship is difficult. Some feel more comfortable condemning themselves totally than accurately assessing their strengths and weaknesses. They are usually defeated by a sense of futility before they play the first note. Others believe themselves as better than they are, not wanting to face the gap they need to work on. Their performances tend to be hit and miss, but they rationalise that there best performances are how they really play, and their worst performances are flukes. It’s not really them! In this way they avoid fixing and cleaning up what needs to be fixed and cleaned. In either case, the disclosure of  flaws in their playing hurts. because there is so much emotion attached to the flaws, the latter group would try to overlook them, and the former would use them as evidence that they stink. Improvement is delayed for year or perhaps forever”

(Kenny Warner, Effortless Mastery, page 53)