I was initially going to type something along the lines of not speaking for others, but then realized that it comes down to projecting your own sense of self-worth. (Yes, projecting without having anything to back it up with is asinine.) In my career there had been a staggering amount of unique hard to replace individuals that simply did not know how to project themselves as valuable - no one realized their importance until they had been managed out, and honestly there was no one else to blame but the folks themselves.