I was listening to an audio-book on insight meditation while walking the dog this morning, and on it, Jack Kornfield was talking about forgiveness. He said, "Forgiveness is giving up hope for a better past."
Often, our anxiety is the result of not being able to accept something that happened to us -- whether it's something that happened during our childhood or maybe a wisecrack someone made earlier in the day. We dwell on it until it triggers anxiety or even hatred. Ruminating about how someone hurt us doesn't hurt the other person at all; it only hurts us. The best revenge is forgiveness.
We can't change our past. Forgiveness is giving up hope for a better past.