It means not dwelling on the past; but, it does NOT mean forgetting about the lessons learned.
Forgiveness is the intentional and voluntary process by which a victim undergoes a change in feelings and attitude regarding an offense, lets go of negative emotions such as revenge.
Forgiveness is different from condoning (failing to see the action as wrong and in need of forgiveness) or excusing (not holding the offender as responsible for the action).
In considering whether or not to work on forgiving someone, look at how much of a burden carrying the antagonism towards that person weighs. Forgiving does not mean condoning nor rationalizing nor forgetting. It means letting go of the negative feelings such as desire for revenge, etcetera. Forgiveness is made easier if one receives a heartfelt apology(s).
A person who does not forgive carries a baggage of memories of the wrong, of negative feelings, of anger and unresolved emotions that affect his or her present as well as future .... not only should one forgive others, but one must also seek forgiveness if one has wronged someone. Forgiveness is to be sought from the individual wronged, as well as society at large.