When will I grow a thick skin? Why am I so sensitive? I can't survive this world.

Why is my worth defined by how I perform at work? I don't like it. I don't want to be like this. I want to be able to sit back and feel good about my existence, to not gauge myself at what happened to me at work. I'm not at work, I'm not getting paid to think about work....why was a treated a certain way by a certain boss, why was I told off by a more experienced staff member, etc.....why does it bother me? Doesn't it happen to most employees all over the world??? I'm not special. It happens to everyone all the time. So why can't I be happy in my own skin???? Why do I define myself by these experiences, or my failures?