GUILT.
Guilt is a man-made emotion. It is not natural. If you kick the dog for chewing up your slippers he ain't going to feel guilty about it. He's not going to chew on them anymore because he doesn't want to get kicked again, not because he feels guilty. Also, he realizes that this upsets you.
Guilt is negative and useless. You can do nothing about guilt. You cannot act upon it. It festers and torments you with no positive results whatsoever.
"Rolling in the muck is not the best way of getting clean"
Humans are the only creatures who experience guilt. It is NOT a natural emotion.
However, remorse or regret (like the dogs) are useful in making us better spiritual beings.
Learn from you mistakes and make up for wrong doings. If you messed up then learn from it. "Behave better next time."
We have total control of the here and now and can help mould the future.
Unless you're HG Wells and have a full-on, working time machine then there is absolutely nothing you can do about the past. (Certain magicians and shamans accepted)
Everyone messes up, everyone makes mistakes. Everyone, with hindsight wishes they had done certain things differently. Lord knows I feel like that all the time.
All one can do as an individual is learn from the past and try and rectify situations for which they are responsible.
The Buddhists have no word for guilt and oh what a better place our world would be if the rest of us didn't either.