I have a pretty good memory for life events, but I have a history of blocking out certain traumatic events like being molested or suddenly and callously breaking up with people who were still in love with me. Some events I remember now, some I don't.
I thought I only blocked out traumatic events until I recently realized that I did the same thing in childhood with quite a few little everyday events. When I was a kid I worried that I was going crazy. At six, seven, eight, I didn't think of it as insanity, exactly--I'm not sure I had a real grasp of what that meant--but I was deeply troubled and frightened by it. So I didn't tell anyone about it.
The mind is odd. With some of those forgotten events, I was able to sort of create memories, fill in the gaps with something I made up. It made me feel less scared.
My mother also had a habit of coming into my room and removing items (like books and comic books and occasionally toys) that she considered to be inappropriate for me. I didn't realize this until I was ten and I actually caught her in the act of throwing away a book that a schoolmate had lent me. After that, I mentally blamed her for all of the little inexplicable weirdnesses, the objects that moved around in my room as if by magic, the things that disappeared, the items that were defaced. That, too, was a defense mechanism. I needed a scapegoat.
But, seriously, why would she draw pictures on the box of my favorite board game? write stuff on the bathroom mirror with toothpaste? put my watch into my toy oven instead of on the nightstand? move various other objects to different places? She was messed up, but the wasn't messed up enough to do stuff like that. So I figure it must have been me.