The regret and sorrow that so many people feel from time-to-time typically has everything to do with the actions that they have done to others, which in its effect, are readily categorized as evil, because it has either hurt the other, or taken advantage of the other or are clearly bad acts that are not becoming of someone of good character. In other words, as much as we might temporarily delight in our bad actions which may have produced for us, at the moment, something that we desired or wished for, the end result after further reflection, or from the aftereffects of such, is ultimately going to be sorrow for having done it, for given into an action that we should have had the integrity of character to not perform.
Whenever we are provided with the opportunity to perform good actions, but instead revert to performing actions which we pretty much know are evil because there are entirely self-serving or morally wrong, but insist that we have to do this, there is going to be for a certainty, a reckoning, and that reckoning, will bring consequences. That is to say, to believe somehow that the doing of that which is wrong will not ultimately be reflected in how we are viewed and how we are judged is the type of fundamental mistake that brings sorrow.
The things that we regret most are always going to be those things that we should have done, or could have done, but did not do, and because we did not do what we were meant to do, we feel disappointment for doing wrong. This signifies that those who play the short term, enjoying their sins at the expense of being virtuous for the long term, are going to find that this choice, freely made, has exacted a price, and that price will be paid, sooner or later.
The best way to overcome evil is always going to be to do good, of which, each decision that we make day-by-day reflects whether or not we are progressing to the only brightly lit destination that matters, in which there will be no regret, or whether we are stepping ever further into darkness, in which our successful escape will require a renewed effort to make good by doing right.
So then, the sorrow and regret that we experience in our being, is only going to be overcome by our proactive actions done for the betterment of the society that we are a member of, which will mitigate what has occurred, to be replaced by good deeds, done for the right reasons, to overcome evil with that good. That which is evil is the opposite of that which we were meant to express in our actions, and because we have done the wrong thing, we are unable to rise to the level so necessary to have peace of mind and peace of our being, signifying that the sorrow that we wish to be relieved of, requires our concentrated effort and discipline to stay on the straight and narrow path and not to deviate in our sacred mission to not only do the right thing but to be the right thing, as well.