This question is one that hits me very directly as it is connected to my permanent condition as an Autistic... We in the Autistic Spectrum tend very much to overemphasize our shortcomings and belittle our capabilities - it's just one of the expressions of how our brain is functioning. I don't say that only we experience this; but most of us are more prone to thinking we are not good enough than Neurotypicals. I'm looking at my own example: I finished my Leaving certificate with best marks, being third in a class of 129; I completed undergraduate university in record time with an MA in history as third of a class of 355. I then completed my PhD in record time - less than a year - coming second in a class of 88. And yet I always sought after becoming better still because being second was already a cause for depression - I was simply unable to put my achievements in relation to what others managed to do. Even when I reached the absolute pinnacle of my chosen profession and was awarded a Professorship in Trinity College, Dublin, Ireland, I was not content. I could not strive for more, but there was that nagging thought I was not good enough... it ended with a divorce and deep depression; several years of therapy which did not help me at all because the therapists did not recognize the root of the problem, i.e. my Autism (and please forget everything about Rain Man and similar movies: There are such people about, but they are at most one % of the Spectrum). Only when one clever psychiatrist, at the goading of my wife, took the trouble of testing me for Autism did I suddenly receive the master key to everything that had ever happened in my life, and to my own mind. Since then, I have found the key to compromise and happiness; and now, I am not driven any more to try and reach unattainable goals, but am content to be what I am, and - in music - to be a good player within my own comfort zone. I still try to do as well as I can; but I now accept my own limitations while still trying to improve. And I am happy that way.
Hope you could make some sense out of this.