Regret is the emotion of wishing one had made a different decision in the past, because the consequences of the decision were unfavorable. Regret is related to perceived opportunity
Why do we regret? … Feeling regret reminds us to think carefully about our decisions and helps us not to make the same mistakes again. Regrets are also how we learn about ourselves, and know what it is we really want. In feeling regret, we have clarity about what outcome and things we truly want for ourselves.