Regret is a powerful and potentially devastating emotion.

In 1995, a Liverpool man who regularly played one set of lottery numbers failed to renew his ticket during the week his numbers came in. Thinking—wrongly as it turned out—hat he'd let a prize worth millions slip away, he committed suicide.

We can't know what he was thinking, but we can imagine that his emotional distress was compounded because he felt personally responsible for the outcome. And that is one definition of regret: Recognizing the difference between how things are and how they might have turned out—if only we had made a different choice.

Since the late 1990s, the study of regret has benefited from the availability of advanced neuroimaging techniques. We have evidence that parts of the brain responsible for reasoning and emotion become active when a person experiences regret. In particular, an area known as the orbitofrontal cortex (OFC), located in a region of the brain responsible for reasoning, may carry out the essential task of comparing real outcomes with imagined alternatives. Brain scans demonstrate increased OFC activity when people experience regret. And patients who have suffered injuries to that part of the brain are unable to experience or learn from regret.

Much of the literature on regret discusses its negative impact. It's considered stressful and may lead to physical illness. It may be amplified by depression, or it may be a cause of depression. Exaggerated feelings of regret are associated with a poorer quality of life in later years. If one fails to learn from experiences of regret, the outcome may be misery, self-destructive behavior, or—as in the Liverpool case—a fatal act.

But a study highlights the benefits of regret. Colleen Saffrey at the University of Victoria and colleagues at the University of Illinois, writing in the journal Motivation and Emotion, provide evidence that people actually have a high regard for regret.

In one study, subjects rated regret favorably in a survey, indicating that experiencing this emotion helped them make sense of life events and come up with a remedy for what went wrong. In a second study, the researchers asked subjects to reflect on 11 negative emotions —such as fear, anger, anxiety, and shame—in addition to regret. The subjects rated how much they agreed with statements about the value of the emotions, for example, whether an emotion "helps me know how to act in the future" or "improves my relationships with others." Across the board, regret was the most highly valued of the negative emotions studied.

Regret has an important social context, too. We learn not only from our own mistakes, but from the mistakes of others. We also learn about preferable outcomes by seeing our peers, colleagues, or neighbors make favorable or unfavorable choices. This may engender envy or relief, but—either way—it helps us figure out how to improve our lot.

The literature is persuasive on the importance of regret in decision making. The power of regret may explain why few of us are very good at objectively appraising risks and benefits. Rather than looking forward to figure out what is in our best interests, we typically look backward. We reflect on what has and has not worked out in the past. Then, whether we are deciding about a life partner, a career, a financial investment, or a medical treatment, we choose the option we are least likely to regret.

Managing regret productively may be an essential ingredient for mental health, a good quality of life, and a positive sense of well-being. If that's true, it is worth continuing to make it a focus of research and therapy.

—Michael Craig Miller, M.D. Editor in Chief, Harvard Mental Health Letter