Regret is a negative conscious and emotional reaction to personal past acts and behaviors. Regret is often a feeling of sadness, shame, embarrassment, depression, annoyance, or guilt, after one acts in a manner and later wishes not to have done so. Regret is distinct from guilt, which is a deeply emotional form of regret — one which may be difficult to comprehend in an objective or conceptual way. In this regard, the concept of regret is subordinate to guilt in terms of its emotional intensity. By comparison, shame typically refers to the social (rather than personal) aspect of guilt or (in minor context) regret as imposed by the society or culture (enforcement of ethics, morality), which has substantial bearing in matters of (personal and social) honor.
It is also distinct from remorse, which is more direct and emotional form of regret over a past action that is considered by society to be hurtful, shameful, or violent. Unlike regret, it includes a strong element of desire for apology to others rather than an internal reflection on one's actions, and may be expressed (sincerely or not) in order to reduce the punishment one receives.
Regret can describe not only the dislike for an action that has been committed, but also, importantly, regret of inaction. Many people find themselves wishing that they had done something in a past situation.
There are extremely specific models of regret mostly in economics and finance under a new field called behavioral economics. Of these, the most clearly emotional is buyer's remorse, also called buyer's regret. Other examples include regret aversion or more generally, regret (decision theory).
Existential regret has been specifically defined as 'a profound desire to go back and change a past experience in which one has failed to choose consciously or has made a choice that did not follow one’s beliefs, values, or growth needs'.