Why does someone who is insecure hurt so much more when someone else says they are worthless than when I say it?

It's my boss, she left a really really critical email to my bosses boss about me where I would stumble upon it. She obviously thinks I am an abject failure. It hurts mostly because I fear failure so much having someone validate that fear with open disdain really cuts me deeply. I want to quit. I want to run away. I want to attack her verbally, even physically. I cannot because I need this job but isn't this why they can treat us like shit? Because we all feel like we need the jobs??. I hate what I do and I hate not being enough to doit well enough @Robynthebeautiful

@Genieinabottle Wow. I see what you mean now. This is a really tough one and you are stuck.
I know its easy for me to say but try to prove that email wrong and make your boss wrong.
Have faith in yourself and just do the job you where hired for.
When worried about making mistakes, you will make mistakes.