When a person is offended they may experience varying reactions such as anger, hurt, humiliation or annoyance.  Generally speaking, the greater the perceived offence the stronger and more persistent the emotional reaction will be (Lazarus and Averill 1972).  The person's appraisal of the trigger event may be accurate (he was discourteous), exaggerated (he's doing this to wind me up) or excusing (it's not his fault).  Past schemas may influence the appraisal, for instance someone constantly ridiculed as a child may 'read' the trigger event in an overly personal way (everyone is unpleasant to me because I'm so useless) (see emotional processing model).  The type of appraisal will shape the emotional reaction (Ortony, Collins & Clore 1988, Beck 1976, Oatley & Duncan 1994).  For instance, the appraisal 'they did that to show they are superior to me' might make the person want to prove their worth more than the appraisal 'they did it because they didn't understand'.'  Some events such as assault or rape can hardly be anything but aversive but may be overlaid with a range of personal appraisals by the person.

Emotional processing involves absorbing or dealing with the perceived hurt/offence so that it no longer irks or distresses the person.  This is partly a conscious and partly an unconscious process (see mechanisms underlying emotional processing).  The attempt to absorb the irritation may involve mental rumination - replaying or going over the event, reasoning with oneself about it, attempt to understand it or see it in a different light.  This might be called 'healthy rumination' (Philippot & Rime 1998) with the end result of reducing the feeling of aggrievement.  However, one of the problems with mentally replaying the offence is that the person re-experiences the sense of being aggrieved and sometimes the rumination may not serve to process the hurt but rather aggravate and extend it (Kross et al 2005)

A sense of justice and injustice seems to emerge early on in child development.  The well worn cry of 'it's not fair' suggests that child has a sense that justice has been violated.  Worthington described the importance of the size of the 'injustice gap' in determining the degree of outrage felt.  It is natural for people to want justice to be done, redress or punishment made and reparation of the damage.

Forgiving the person is like mentally dropping the charges against them or 'letting them off the hook'.  The person accepts that they have been wronged but will no longer demand the (imagined) trial, sentence and punishment of the offender.  Where the perceived offence is great this is not easy to do.  Worthington and others outline some of the possible benefits to health of forgiving others.

Unfortunately in rumination, when the person mentally replays the memory of the offence they can derive a certain pleasure or savouring of their revisited aggrieved emotion.  Like Gollum fondling his 'precious' ring, this savouring can go beyond healthy short term rumination to become a grudge.  The terms 'holding a grudge' or 'bearing a grudge' imply holding something to oneself or failure to let it go.  This is discussed more fully in 'Ruminating your life away', Chapter 12 of 'Emotional Processing; healing through feeling', Dr Roger Baker, Lion-Hudson, Oxford.

The positive benefits of holding a grudge are that one maintains a continuous sense of justice - the offender is continually held accountable and one can savour the feeling of injustice.

The negative must be that it makes an investment of at the least mental energy, and at the most stress, to maintain the grudge.