If we forgive the pain has gone, we do not need to carry it. Whatever happened, it happened, and the moment we accept it and move forward with forgiveness is the moment the pain will go too. The moment and the event has gone, and is in the past. Now is all that matters.
It allows closure, we choose, we allow ourselves to let go, to be free of the mind and its desire for retribution. The ego wants revenge, the soul wants peace.
Acceptance and forgiveness go hand in hand with inner peace, healing and joy. We may not be happy about what happened, however, even if the surface of the water is turbulent, the bottom of the sea is always calm.
That is the same with us when we forgive, we are the calm of the deep ocean, when we fight and allow hate, revenge, anger and other emotions to come, then we become turbulent like a sea in a storm. We can be unhappy but still be at peace with it, only when we let go.
Forgiveness is not easy, but it is better than a lifetime of pain and hate for something we can never change.