Confidence.

Caravaggio, Narcissus, 1603

If one really has confidence in oneself, one doesn’t feel the need to boast. It’s because one’s feeling of inferiority is strong that one boasts. One feels the need to flaunt one’s superiority all the more. There’s the fear that if one doesn’t do that, not a single person will accept one “the way I am.” 

Ichiro Kishimi, from The Courage to Be Disliked