"Regret is an emotion, and it is also a punishment that we administer to ourselves. The fear of regret is a factor in many of the decisions that people make ("Don’t do this, you’ll regret it" is a common warning), and the actual experience of regret is familiar. The emotional state has been well described by two Dutch psychologists, who noted that regret is "accompanied by feelings that one should have known better, by a sinking feeling, by thoughts about the mistake one has made and the opportunities lost, by a tendency to kick oneself and to correct one’s mistake, and by wanting to undo the event and to get a second chance". Intense regret is what you experience when you can most easily imagine yourself doing something other than what you did."
— Daniel Kahneman, Thinking, Fast and Slow