Quoting Steven McDonald, a NYPD officer shot by a teenager and paralyzed:
When I was a very young kid, Dr. King came to my town in New York. My mother went to hear him speak, and she was very impressed by what she heard. I hope you can be inspired by his words too. Dr. King said that there's some good in the worst of us, and some evil in the best of us, and that when we learn this, we'll be more loving and forgiving. He also said, "Forgiveness is not an occasional act, it's a permanent attitude." In other words, it is something you have to work for. Just like you have to work to keep your body fit and your mind alert, you've got to work on your heart too. Forgiving is not just a one-time decision. You've got to live forgiveness, every day.
Source: Johann Christoph Arnold - Why Forgive?, pp.181