Forgiveness

I had a thought today during Sunday school. Why is it so hard for some people to forgive and it seems easy for others to forgive? Isn't it true that all it does is hurt ourselves to carry around that anger and pain? Why can't we just let it go? Forgive and forget! You hear of stories when people forgive the unforgivable. I know a man in my ward who's father was murdered and he has forgiven the man who did it. I am amazed at that.
I am not one to hold grudges. My sister Annalisa once told me that when I get mad at her, she doesn't care that much because she knows I will forget about it soon. I think part of that has to do with my bad memory and part of it has to do with the fact that the small things really don't matter in the long run. I used to get really mad about the small stuff such as when someone cut me off while driving or when someone said something rude to me. In my old age I'm learning to not let those petty things get to me. I get upset at first but then let it go. Or at least I would like to think I do.
I read this book called 'A New Earth' which I recommend to anyone. Something that has really stuck with me is this: When someone offense you or has wrong you, let it go! Don't go 'vent' to someone and talk bad about that person. Just let it go. All venting does is hurt yourself. It creates more negative energy for you. Talking bad about that person and harping on it only hurts you in the end. It does nothing to the other person. This is something I've been working on.
I really admire people who forgive the unforgivable. How do they do it? How do you let the big stuff go? I would like to think that I'm getting better at this but I hope this is something I will be able to master my life time.