One common ailment that musicians go through is “not good enough”-ism. For non musicians this may be a new concept, as the media portrays most famous musicians as cocky and elitist. Although that definitely exists, there are quite a few musicians that have a problem accepting praise and with positive self-talk. Constant personal attacks on yourself is not humility.
Negative self-talk will hurt your self-esteem, make you look weak, hurt your musicianship, and even increase the frequency of mistakes. So why do you do it? You likely talk to yourself much worse than you would talk to a friend. If you learn how to be your own best friend, you’ll be a happier and better musician.