(this thought started life as an e-mail from me, but I liked it so much I told the reader I was going to steal it and post it on my blog)
The past is always a hard thing.
Good or bad, it's done and can't be changed. Some people are good at facing it, some people want to bury and pretend it doesn't exist. Some people are really accepting of others' pasts, and some people can't get past it and let it color their judgement of people now, or they want nothing to do with other people's pasts.
But, without our history, we are nothing. Every experience, every person has touched us in some way, good or bad to make us exactly who we are now. I love all that space-time continuum... butterfly effect... back to the future... etc. Change something, no matter how seemingly insignificant and major ramifications could be felt forever. I guess that's why it's good that we can't change our past. All we can really do is learn from it, and embrace it as part of who we are. If we are ashamed or unhappy about our past, all we can do is make sure the new pasts we make each day are better than those before them, I guess. (Yeah, pasts isn't a word.)