As a child I wasn't taught how to stand up for myself. Sometimes when I tried I was beaten. Sometimes when I tried I was made to feel my opinion didn't matter and I was taken advantage of. I'd rather be beaten.
When someone thinks I've done something to hurt them, or when they are just angry at themselves and see me as a victim. I might think it safer to keep to myself and say nothing.
Often that may be exactly the right thing to do.. but sometimes people take advantage for a long time. When I ask why they don't want to tell me, so that says something. However, I must still be allowing myself to be taken advantage of.