From The Lion King:

(Rafiki and Simba standing on a plain, talking)

Simba: I know what I have to do, but going back means I'll have to face my past.
(or something to this effect)

(Rafiki hits Simba on the head with his stick)

Simba: (startled) Ow! What'd you do that for?

Rafiki: What does it matter? It's in the past!

Simba: (rubbing head) Yeah, but it still hurts!

Rafiki: Ah, yes, the past can hurt. But the way I see it, you can either cry about it, or, learn from it!

(Rafiki swings stick at Simba, who ducks)

Rafiki: Ha ha! You see? Now, what are you going to do?

Simba: Well, first I'm going to take your stick.

This is a lesson everyone should learn sooner or later, I believe. Almost every single person has had something happen to them in the past that pains them to think about. Yet some continue to make the same mistakes over and over again, because they would rather ignore the past instead of remembering and learning from it.

Hence all the 'Lest We Forget' things about war.

"But it hurts too much to think about!"
I have both heard and used that argument. I too have used the Freudian defense mechanisms: Repression, Denial(oh, that's been a big one. Ask my once other-half. He could rant for hours on that), pretty much all of them, I guess. I took a psychology course.. I feel so special wheeeee...

What I'm trying to say (in more words than necessary, as usual), is that dwelling on the past, or trying to ignore it, is merely a state of mind and can be "cured", if one wishes.

Don't regret what you've done. Learn from the experience]. Mistakes are simply opportunities for learning: kid burns himself with stove, learns not to touch hot burners. Kid cuts himself with knife, learns to respect sharp things and be careful with them.
The same principle applies to everyday life experiences: don't regret what you can't change. The past is already written in stone: just go over the stone once in a while to make sure you're not repeating yourself. If you find you are, look at why. Self-analysis is a wonderful thing. The more you do it, the better you become at it. You'll understand the reasons behind those things you just didn't get about yourself, once upon a time.

I don't know about you, but I find it really interesting to reflect on myself and think, "Oh. So that's why I did that."

If I weren't so antisocial I think I might have made a pretty good psychologist (or sociologist; they're both kind of cool)

I'd like to think I don't need a reason. But deep down inside we all have one.