There are many times in life when we make choices we wish would have never happened. They make us grimace and sometimes even cause us more pain that what we thought we could bear.
But the wonderful thing about life is that with each day it brings another start. Another try at what we set out to accomplish. There is no "It's a Wonderful Life" type miracle, and the pain may stay for longer than we hoped for, eventually there is a point where we have to move on.
We look our mistake in the eye, shake our fist at it, say "Never Again," and (if we are lucky) really mean it. Of course there are always obstacles. Life would be half as rewarding if it were a cake walk. But the do-over allows us to be human, make mistakes and hopefully, for most of us, learn from our past indiscretions. And knowledge is the most powerful tool we can harbor.
The situation may be small or to an extreme extent. The *groaning* "I shouldn't have done that..." could be a momentary slap in the forehead or something more painful that lasts a while. The times where the mistakes seem to never leave your mind, can really grade on you and wear you down. If it is a BIG one, it's probably the hardest thing you will ever accomplish getting over the "I wish it wouldn't have happened." But take heart and pride in the fact that the all natural human behavior of making said mistakes are just that.
Know that once the smoke clears, the sun breaches the crest of the next morning and the memory fades into something a little less harsh, you will learn to come to terms with it; then we can truly be free.