When you are feeling overwhelmed by your inability to forgive some wrong or injury done to you, remind yourself of the ancient teachings about laws of karma that are echoed in Christian teachings: What goes around comes around - in this life or the next. It is not for you to decide the nature of justice on a personal level, which is just as well, since human justice is often much harsher and less well balanced than Divine justice. Your only task is to learn to forgive - and call back the energy you are wasting on events in the past.