Have most people witnessed or experienced something that deeply disturbed them for life?

The more you focus on it, the worse it's going to get. People push away these things by creating new, positive experiences and filling their life with things that make them feel good and connected to other people.

I'm sure plenty of people saw/heard or even experienced something disturbing as children that formed their deep-rooted beliefs and judgements about things in life but I believe that some of them are able to lift the veil and see their own bias.

Anyway, I think I get you. I had a phase when I felt like I couldn't get over something from my past. I was hypersensitive to anything related to the topic, if someone mentioned something about it I stormed with rage at them telling them to shut up, if I read something related on the internet, I hyperventilated and cried, I felt like other people could never understand me because they never experienced these things, which is true but unlike then, it doesn't matter to me that much now. You just need to reach the point when you get reconciled with the facts and become less emotional about it all. It'll never go away completely but the more you will poke into it the more it will snowball and more sensitive and emotionally unbalanced you'll be not just about what is personal to you but also about problems of other people.