Struggling to Forgive: Why Can't I Let Go?

It's hard to say what's normal and what should be normal, but for me I definitely feel that way for some grudges. I try to remind myself that I have been able to let other grudges go more easily, I wonder if you feel the same? I know it's much harder to forgive some one who doesn't show any remorse or keeps engaging in the same problem behavior. In that case, maybe you don't need to forgive them but take it as a sign that you should move on from them. I also wish I had an easier time feeling people's approval. I know I'm currently trying to let go of focusing on that so much and instead focusing on my own approval of my self.