Regret is one of the most cloying, self-wounding sensations a person can experience. It can also be, if viewed with proper perspective, the most useful mechanism to achieve what you wish to achieve. I shall outline the benefits in three forms: Minor, Major, and Euphoric.
Regret lends you the experience and capacity to modify and improve your behaviour when faced with a scenario you regretted your actions upon before. This is because, in essence, regret is not hopeless - in order for it to be regret, in order for it to sting, there needs to be the sense that we could have done better. If someone unexpectedly shoots us and we fail to dodge the bullet, we do not regret this lack of skill because it is beyond our hypothetical means. However if someone throws a water balloon at us and we fail to dodge it we are afforded some measure of regret, as we have the notion that what transpired was avoidable. If viewed in this way, and then applied to a future hypothetical scenario, regret has the chance to metamorphose from a stolid, dour, emotional caterpillar to an optimistic butterfly. You didn't act within your capacity, it says, but you can. At it worst, you get stuck on the first part of that sentence. At its best, you discover the second.
In a sentence: you do the same thing better.
For example, you are running in a 10km race. Calculating your fitness, you figure you can run full speed for the last 400m only - any more and you risk not completing the race at all.
You run the race, and at the last 400m you run at your full capacity. You finish the race in 5th place - not terrible, but not what you thought you could do. Worse still, you look around at all the other runners - they are all at their limits, puffed and staggering. You are not. You have the unnerving thought that you could probably run further, for longer. You should have started your final spring far earlier, like 800m or so, and given it all you've got. You misjudged your own capacity, and as a result, you feel regret towards the scenario.
The next year you run the race again. Vowing to not make the same mistake, you increase what you view as your limit, and give it your all. You come in first, but more importantly, feel thoroughly breathless by the end.
This is the minor benefit of regret.
After you finish the race you take the bus home. You sit in the back contemplating your mood - which you soon realise is too slippery to hold, so you simply sit and pay attention to the faces of those who enter and leave the bus. As you look at each, you start to imagine their lives. Eventually it's your stop, and you leave the bus. You arrive home. You take the letters out of your mailbox and hold them under your arm so you can carry your equipment as well - when you place them on the kitchen table, they are soaked in your sweat. You look at your name on one of these envelopes, typed in Times New Roman 10pt. You get out your mobile phone and call your boss to tell him you're quitting.
The major benefit of regret is that it affords us the capacity to not only reconsider how we approached one specific situation which we did not live up to our potential, but also to other neighbouring ones. If we feel regret over a race ran poorly due to misjudgments of our own toughness, this regret can be turned into the statement: "You know, you are tougher than you think you are."
If, in our working life, we have only ceased in not quitting our hated job due to the fear of how we will manage without it, and an absence of any confidence to grow and find a better job, then such a statement, torn from its initial roots but still beholding the same sentiment, can be the very impetus we need to give ourselves greater credit, and do what we truly desire.
The night you finish the race you barely sleep. This is made all the more distressing because you should be dog-tired due to the race, and your persistent waking energy serves to remind you of the mistake you have made. Not only did you not run hard enough, but really, you've never run hard enough. The feeling gnaws on you while the ear-splitting shriek of silence pushes you further and further into your own head.
Suddenly you sit up. Suddenly, it seems, you've had enough. But what do you do now, suddenly?
You find yourself running through the streets. You are in your pajamas and slippers, but you run surprisingly well all the same. The air is cold but its sharp tinge starts to give way to the warm sweat now dripping from your forehead. Finally, you reach your destination.
You forgo throwing tiny stones at your lovers window, realising it is not particularly hard to scale the vine covered wall and go up there yourself. Your hands and now slipper-less toes grip whatever it can as you climb - bumps and nobbles press your cold, bare skin, but you keep climbing. You reach the window, and jar it open.
Your lover sits up on their bed, somewhat terrified. You tell them, quickly, breahtlessly, that you were wrong, that you were only afraid, that you will marry them.
They switch the light on. You both blink. They ask you if you've gone insane. Yes, you tell them, but you still want them all the same.
The euphoric benefit of regret is that, in giving us these deeply negative feelings, it gives the potential of a torrent of motivation to never feel regret again. Of course you will feel regret again, since we are always less then perfect, and always make mistakes. But the euphoric benefit is a temporary surge to now do only what you truly desire. The minor benefit tells us that we can do the same situation better, the major benefit tells us we can do other parallel situations better - the euphoric makes no statements upon your own potential or upon any situation, it merely exclaims: "I don't want to feel like this!", and gives you the energy and the drive and the fearlessness to then live true to yourself. Because it is the vaguest, the euphoric benefit of regret is the riskiest, the least accurate, and the most insane. It is also the most fun.
I am not suggesting at all that regret in itself is good for you. It merely, if viewed in a certain light, creates the potential to live your life truer to your own desires and less to your fears. I don't wish to write about what usually happens with regret, how we don't always pull these potentials from it, because, simply, you know what that feels like, I know what that feels like, we all know all too well what a useless caterpillar of regret can sometimes feel like, when we never let it crawl on, and pupate.
Also, this only all works when we have the ability to accurately perceive our own capabilities - if we, to use the earlier example, forever believe we can dodge that bullet, then we will forever be disappointing ourselves. Unfortunately it is often in our lives where we are incapable of this. Regret, then only serves to drill us deeper into the ground.