In this study we explored the prevalence of regret following uncommitted sexual encounters (i.e., casual sex that occurs with someone once and only once or with someone known for less than 24 hours) among 138 female and 62 male Canadian university students, who were approximately 21 years of age. The majority of participants self-reported that they had experienced feelings of regret after an uncommitted sexual encounter. We found women reported feeling significantly more regret than men. However, men's regret was more closely tied to physical attributes than women's regrets. Regret was also influenced by the quality of the sex: high-quality sex rarely led to regret, while the reverse was true for poor-quality sex. In keeping with past studies, intoxication by alcohol and/or drugs was often listed as a source of regret by both men and women.That is the abstract of the paper "Feelings of regret following uncommitted sexual encounters in Canadian university students" by Fisher et al (January 2012) (not available online).
These are some explanations of regret I have encountered:
One can argue that regret is a positive feedback (it is one of those feelings that makes us humans). It is a natural mechanism that reminds us of our mistakes. It tells us that we can do better. This description avoids explaining why some people are more regretful than others.
Others argues that regret is the consequence of having expectations that are too high when matched with reality. This explanation does not say why some people have higher expectations than others, or if learning occurs (why people might not learn to reduce their expectations through time).
Some even argue that regret should be treated like a visitor. One should be a good host and eventually regret will depart. This explanation does not say if regret departing is the effect of a natural process or if it is the consequence of purposeful thinking.
Of course "excessive" (or "lack of") regret might be due to certain cognitive processes which I (we) do not understand so far.
Of course the literature on regret is huge. It includes recent contributions by behavioral economists like Daniel Kahneman. He argues that the experiencing self and the remembering self perceive reality differently and this matters for happiness (and regret I presume).
What would be an economic approach to regret?
First, it could play an evolutionary purpose: to improve decision making - even if the process takes generation. In the same way that the feeling of happiness is a payoff of a good decision, regret might be the payoff of a bad decision (the size of which depends on the benefits and costs involved). Regret can be therefore an inevitable consequence of living in an uncertain world where decisions have to be made. Add computational limitations of the human brain and regret is a sure outcome in some occasions.