A Dark Feeling That Grows Like a Tumor
Eventually I had to forgive that dealer, not for his sake, but for my own. The well justified hatred I had for that person was not benefiting anyone, least of all myself. That is part of the reason that Jesus emphasized forgiveness so much, because retained anger becomes hatred and hatred is a cancer that grows until it consumes you.
A justified hatred starts out as anger over a wrong-doing or dramatic failure that hurts you or a loved one. If there is no satisfaction found and forgiveness the anger grows until it consumes more and more of your thoughts. Soon you reach the point where it is infecting other thoughts and you become obsessed with it. You become angry at those who don't share your anger because they "obviously don't care." Soon the anger becomes the primary driver of your life and once it dominates all of your thoughts, you and your anger become one and the same.
There was a guy I used to work with who was a decent, likable guy. I forget what led up to it but he became a union fanatic and when the union failed to deliver he got angry. He hated management and he soon came to hate those who didn't hate management. He shouted obscenities at those who didn't vote the way the union instructed us to. By the time he left I could no longer call him a decent, likable guy; he was a bundle of anger and hatred and little more.
I have seen it at both ends of the political spectrum when hatred supplants reasoned discussion. It's normal to disagree with a politician, even to dislike them, but when anger turns to obsessed anger, which turns to hatred, no good will come of it. You read it at Daily Kos where leftists are unhinged with their hatred and anger. There are also a few conservative bloggers who burn with anger at anyone who does not share their out of control rage at the GOP for not nominating a real conservative. Such a person is a threat to their own spiritual well-being.
Forgiveness is hard. I know it is. But it is for the benefit of the forgiver as much as for the forgivee. Letting go of anger is hard. Letting go of hate is hard. But if you don't you will become very much like what you hate.