It is hard to forgive without letting go. To let go is to not demand what is owed you. To let go is to unburden yourself with the task of trying to make someone else pay for what they have done.
There seems to be an injustice to it, this business of letting go. Why give up what is rightfully yours? Why not go after someone and force him to give you what he is obliged to do in the first place?
The answer is PEACE. Peace for yourself. The kind of peace you need so you can move forward and not be shackled by the past transgressions of other people.
Not every battle can be won. There are some things we lose, some things we must give up. But there are some things worth saving, and our peace of mind is just that. It is something we owe to ourselves, something important to our eternal and priceless soul.