Forgiveness

How the fuck do people do it? Forgive.
I don't mean for little shit, that's easy. The reasons to forgive little offenses are extensive: Life is too short, no one's perfect, let ye who is without guilt cast the first stone, etc.
What I don't understand is how forgiveness can prevail when there is deep pain involved--emotional or physical. The tendency seems to be superficial forgiveness, when at the core pain and fear remain. Pain from allowing ourselves to be vulnerable in the first place, and the fear of the future.
Maybe we choose to be unhappy, and the power of NOT forgiving is a way for us to hurt ourselves indefinitely...like a wound we can reanimate whenever we want.
The past is a strange thing. According to quantum physics, our brains cannot tell the difference between something it remembers and something it is experiencing in real time. That makes sense to me, because painful things in my past cause real time pain when I think of them. The question is, why do we think about the fucking past? The past is not a reality. Our perception of what WAS is never exactly the same as how others remember what WAS. Therefore it is not something tangible.
Of course when things are recorded with audio/visual equipment and retransmitted we believe we understand what happened in the past. Does that make the actual events from the past real, though? Does that make pain and fear more justifiable?
Lately my dreams have been loosely tied to events from my past--like an alternate present that is heavily influenced by pain from my past. Waking from these dreams is difficult. I find myself reminiscing on painful memories for days, and this is the motivation for my current web logging.
Truth be told, I don't enjoy pain.