MargenA grudge is a tenant who pays the rent with your sleep. And it never, ever moves out on its own.
The curious thing about a grudge is that it feeds on you while you believe it is punishing someone else. The person who hurt you sleeps soundly in another city; you have booked them a room in your head, with a view, heating and breakfast included.
Forgiving is not absolving anyone. It is changing the lock and taking the room back to live in it.