Because I'm not someone else

No one really hate themselves at first. Has anyone said they hated themselves when they were a kid (below <6 yr). I’m sure the answer is no. As we grow up society imposes their standard of what is expected and what’s not. We judge ourselves based on what society deems is attractive or not. If we don’t meet this standard we feel depressed. Whole business are built based on this conundrum model. Look at tooth braces, look at shoe lifts, look at hair extensions, Botox, plastic surgery...etc.

The lack of self knowledge

The discrepancy of one's expectations of one's self and the reality of one's capacity.