I think it is forgiveness. I also think it can be a little bit foolish to forget some things/actions by others. We have all been hurt. It is interesting though that we can forgive and forget a major thing that might have happened in the recent past, but then be able to forgive by not forget something that happened years and years ago. And I also believe that just because I don't see karma gettin' the person who wronged me, doesn't mean karma didn't get them. It just means karma didn't think I needed to know about it =D
I think this is a question we have all struggled with at one time or another. Journaling helps me in this kind of thing. So does writing the person a letter as to why I cannot forget BUT not sending it. I actually tear it into tiny little pieces after I write the letter which makes me feel oh so much better.