[H]e was horrified at what he saw behind him: days and days laid end to end, a few deeds and a great many omissions. And that was the worst of it. He could forgive himself for having taken action, however ill-conceived it might have been, but he would always remember and resent the things he had left undone.
— Gabrielle Roy — 1947 —The Tin FluteChapter XXX
You can make yourself happy or miserable — it's the same amount of effort.
— Ray Bradbury
Don't let yesterday use up too much of today.
— Will Rogers
Don't worry, be happy.
— Meher Baba
The way past despair and false hope is just letting go. It doesn't improve your odds of survival, but it doesn't waste mental energy.
— James Alan Gardner —Radiant
The Japanese have a saying:
fix the problem, not the blame. In American organizations it's all about who [fouled] up, whose head will roll. In Japanese organizations it's about what's [fouled] up, and how to fix it. Nobody gets blamed. Their way is better.
— Michael Crichton — 1992 — Rising Sun
Everyone has made mistakes. What's important is how one deals with them, both one's own mistakes and those of others.
Worry and regret might seem like different things, but the only real difference is their place in time. We feel regret about our past, and worry about our future. Both are a useless waste of the present.
Worrying isn't the same as concern or planning: those can be useful activities; worry is a waste of time. If we are able to control some aspect of the future it is appropriate to think about how we want to control it. If there are things we can't control, it is appropriate to think about possible outcomes and how we should react to them for our maximum benefit (or minimum harm). But dwelling on the things themselves that we can't control is a totally useless activity.
Imagine that you are waiting for a plane. It might be late. While you are on it, it might crash. It might be delayed and you'll miss your daughter's birthday party. Maybe something bad has already happened to her. Maybe many things. Most of your wait and the flight are taken up with your worries.
Now consider the person sitting beside you. Instead of worrying — and perhaps he has even more things to worry about than you do — he's reading a book or doing work on his laptop. For him the wait and the flight are a productive time.
Both you and he are aware that bad things could happen, but by the end of the trip they either have happened or haven't, unaffected by whether you worried or not. You are both four hours older, but you wasted your time in a totally useless activity while he got on with his life.
Regret is, if possible, even worse than worry. With worry there is at least a small chance that it might lead to something useful (i.e. turning worry into planning), but with regret there is no chance that you will be able to change the past. Despite what is taught by many religions, suggested by parenting guides, or practiced by society, regret is a complete waste of one's time.
Now this doesn't mean that one should ignore past mistakes, nor that one isn't responsible for past actions (or inactions).
If you admit that what you did (or didn't do) had (or could have had) a bad result, you can learn from it and resolve not to repeat the mistake. To the extent possible, you can make amends for the damage. But even if it is something that can't be undone or compensated for, it benefits no one for you to punish yourself; your pain helps no one and hurts you and possibly others. Learn from your mistakes, take responsibility for them, and stop wasting your time with useless regret.
Too many people allow themselves to be manipulated by accepting guilt and the resulting regret from other people. Similarly too many people use worry as an excuse for inaction or as an attempt to make themselves look better. The stereotypical ethnic mother uses her own worrying to induce guilt in her children.
Now is the only time we have. The past is gone forever, and the future might not happen. Fully experience your now and make use of it.
Determining the cause of a problem and letting the person responsible know about it doesn't have to be a process of blame.
Blame is essentially an attempt to force guilt and regret onto another person. Regret provides no benefit at all to its owner and at best provides a sense of revenge to the blamer. If the other person accepts responsibility for the problem (i.e. knows that it was a wrong decision and undoes or compensates for the damage), that should be enough.
How we should treat the person afterward can depend upon various circumstances. If the person is a natural klutz or we feel his only regret is in getting caught, we will need to remember this and use the information to avoid getting into situations where it might make a difference.
You don't continue to lend your property to someone that habitually damages or loses it. You don't continue to lend money to someone that never repays. You don't continue to rely on someone that has proven unreliable.
But if you feel that someone has changed their behaviour or it was a one time happenstance, you can simply forget about the incident.
Either way, these are are changes in your attitude. Continuing to blame and resent the person will do no good, and, like regret, will simply waste your valuable time.
Imagine some bad incident that occurred in high school. You could spend the next twenty years thinking about it, blaming and resenting the person responsible. Then when you meet them at a class reunion you find that they have no memory of the event. You spent perhaps hundreds of hours of your time dwelling on this event and it did not one bit of good. Your hatred doesn't even receive the satisfaction of knowing how guilty the other person must have felt. They enjoyed their life as if the event hadn't happened, while you chose to waste yours.
The whole concept of penance is evil. There is no amount of punishment that will undo what has been done. If you have repented and accepted responsibility, you are already a better person and nothing further can be done. And if you haven't accepted responsibility, all that punishment can do is make you try harder not to get caught next time.
Perhaps the most difficult part of this is being able to forgive oneself. But the alternative is either a lifetime burdened with useless regret, or even worse, a lifetime of suppressed guilt that will subconsciously have serious negative effects on one's behaviour.