Hypothetic: Someone hit me as a child. Being a child, I don't know how to deal with it, but it is unpleasant, so it is natural for me to react in an unpleasant way. I associate unpleasantness with my experience and next time someone tries to hit me, not only do I remember the bad memories, but I still don't quite know how to deal with it, and the after-effects of last time made me swear 'never again'.
If someone hits you and it hurts, you will start trying to avoid it. In any given situation, whatever the premises and the situation is, you will take the necessary precautions. That can mean any of a million different actions being taken, all depending on what situations you end up in later in life.
The effects are truly irrevocable. Everything your brain experiences is just one more thought that you might accidentally pull if you draw a wild card from your head. It's one more memory that you might think of when you overhear someone saying something that is related. Statistically, there are odds that some time in your life you'll end up either being in a discussion or talking to someone where an impression you made earlier in life that was seemingly pointless actually turned out to benefit you. I remember Dante once told me melons are actually berries. I mean it's about five years ago, but for some reason I still remember it. If I had a political discussion about melons, it would probably affect my views, don't you think? Lol.
Let's say your uncle touched you as a child. As an adult, you will be sexually confused. Maybe you feel shameful. When someone playfully accuses you of being a homosexual, you silently feel awkward. When there's a revolution and you become a dictator you suddenly kill all homosexuals for nothing. Mental scars come and go with mental conditions normally. Depression or anxiety. Like with those two conditions, mental scars are not something you can cure. You can only learn how to deal with them so they don't become problems for others.