Certified Armchair psychologist here.

Because you don't love yourself.

And the dumb thing is that people pick up on that and reinforce it, mostly subconsciously but sometimes maliciously.

Just like any relationship, you have one with yourself and you need to maintain it in a healthy way.

And it's hard to do that when you don't have a good self esteem. Be indulgent with yourself, you will make some mistakes and it's normal.