Remorse
Remorse is an emotional expression of personal regret - that is, the emotion felt by the injurer after he or she has injured. Remorse is closely allied to guilt and self directed resentment (e.g. - The boy felt much remorse after hitting the old lady. The idea of remorse is used in restorative justice).
One incapable of feeling remorse is often labelled a sociopath (US) or psychopath (UK) - formerly a DSM III condition. Some researchers have lately suggested that this lack is more characteristic of the INTJ personality, a highly rational temperament that relies very little on emotion, but the scientific worth and psychological accuracy of the Myers-Briggs Type Indicator test have been strongly questioned. In general, a person needs to be unable to feel fear, as well as remorse in order to develop psychopathic traits.
"Buyer's remorse" is the concept of regretting a purchase after the fact of buying it.
Regretting one's earlier action or failure to act may be because of remorse or to various other consequences, including being punished for it.
Expressing remorse
Despite the role apologies play in our lives and the almost daily news reports of the latest celebrity or political apology, there is a surprising dearth of systematic empirical research on the subject of apologies as expressions of remorse.
Two notable exceptions are The Five Languages of Apology by Gary Chapman and Jennifer Thomas, and On Apology by Aaron Lazare. The consensus emerging from these and other studies is quite clear - effective apologies that express remorse typically include the following components: a detailed account of the offense; acknowledgment of the hurt or damage done; acceptance of the responsibility for, and ownership of, the mistake; an explanation that recognizes ones role; a statement or expression of regret, humility or remorse; a request for forgiveness; and an expression of a credible commitment to change or a promise that it won't happen again; and some form of restitution, compensation or token gesture in line with the damage that you caused.
Perhaps the most active research on the relevance of apologies as an expression of remorse appears in the legal and business professions, primarily because of the potential litigation and financial implications.
When an apology is delayed, for instance if a friend has been wronged and the offending party does not apologize, the perception of the offense can compound over time. This is sometimes known as compounding remorse.