It depends what anyone means by "forgiveness".
If it's something like "what you did to me was dreadful, but I don't feel bad about your having done it it now" or
"what you did to me was dreadful but I won't give it/you the power of staining my whole life" or
"what you did to me was dreadful, but you (insert excuse of choice e.g. you couldn't help it, you did it because, I understand why you did it, I'm going to forget all about it, worse things happen at sea et. ad inf)
Personally, I don't think "forgiving" someone else's appalling actions is necessary or useful, and some things can't be moved on from. It's about survival.