Resentment can be triggered by an emotionally disturbing experience that is being felt again or relived in the mind. When the person feeling resentment is directing the emotion at himself it appears as remorse.
Resentment can result from a variety of situations, involving a perceived wrong done to an individual, and often are sparked by expressions of injustice or humiliation. Common sources of resentment include publicly humiliating incidents such as accepting negative treatment without voicing any protest, being an object of regular discrimination or prejudice, envy/jealousy, feeling used or taken advantage of by others, and having achievements go unrecognized, while others succeed without working as hard. Resentment can also be generated by dyadic interactions, such as by being emotionally rejected or denied by another person, being deliberately embarrassed or belittled by another person, or being ignored, put down, or scorned by another person.  Often resentment can begin early, as in the case of children who are unequipped emotionally to respond otherwise to the divorce of the parents.
Unlike many emotions, resentment does not have physical tags exclusively related to it that telegraph when a person is feeling this emotion. However, physical expressions associated with related emotions such as anger and jealousy may be exhibited, such as furrowed brows or bared teeth.
Resentment can be self-diagnosed by looking for signs such as the need for emotion regulation, such as faking happiness while with a person to cover true feelings toward them or speaking in a sarcastic or demeaning way to or about the person. It can also be diagnosed through the appearance of agitation- or dejection-related emotions, such as feeling inexplicably depressed or despondent, becoming angry for no apparent reason, or having nightmares or disturbing daydreams about a person.
Resentment is most powerful when it is felt toward someone whom the individual is close to or intimate with. To have an injury resulting in resentful feelings inflicted by a friend or loved one leaves the individual feeling betrayed as well as resentful, and these feelings can have deep effects.
Resentment is an emotionally debilitating condition that, when unresolved, can have a variety of negative results on the person experiencing it, including touchiness or edginess when thinking of the person resented, denial of anger or hatred against this person, and provocation or anger arousal when this person is recognized positively. It can also have more long-term effects, such as the development of a hostile, cynical, sarcastic attitude that may become a barrier against other healthy relationships, lack of personal and emotional growth, difficulty in self-disclosure, trouble trusting others, loss of self-confidence, and overcompensation.By contrast, resentment does not have any direct negative effects on the person being resented, save for the deterioration of the relationship involved.
To further compound these negative effects, resentment often functions in a downward spiral. Resentful feelings cut off communication between the resentful person and the person he or she feels wronged them, which can result in future miscommunications and the development of further resentful feelings.
Because of the consequences they carry, resentful feelings are dangerous to live with and need to be dealt with. Resentment is an obstacle to the restoration of equal moral relations among persons, and must be handled and expunged via introspection and forgiveness.
Psychologist James J. Messina recommends five steps to facing and resolving resentful feelings. (1) Identify the source of the resentful feelings and what it is the person did to evoke these feelings, (2) develop a new way of looking at past, present and future life, including how resentment has affected life and how letting go of resentment can improve the future, (3) write a letter to the source of the resentment, listing offenses and explaining the circumstances, then forgive and let go of the offenses (but do not send the letter), (4) visualize a future without the negative impact of resentment, and (5) if resentful feelings still linger, return to Step 1 and begin again.
Resentment is considered to be synonymous with anger, spite, and other similar emotions; however, while it may incorporate elements of these emotions, resentment itself differs from these emotions in several key ways. Aside from sharing similar facial expressions, resentment and anger differ primarily in the way they are externally expressed. Anger results in aggressive behavior, used to avert or deal with a threat, while resentment occurs once the injury has been dealt and is not expressed as aggressively or as openly.
Resentment and spite also differ primarily in the way they are expressed. Resentment has the unique quality of being almost exclusively internalized, where it can do further emotional and psychological damage but does not strongly impact the person being resented. By contrast, spite is exclusively externalized, involving vindictive actions against a source of wrong. Spiteful actions can stem from resentful feelings, however.
In Friedrich Nietzsche’s book The Anti-Christ, resentment is used to explain why certain religions view their God as they do. For instance, the Jewish God of the Old Testament changed from the God of the Jewish people to the One True God of everyone because of the oppression of the Jews during the Roman occupation of Palestine. The Jews’ desire to see their oppressors punished spawned a conception of a God to whom all would be accountable, and this conception was driven by their resentful feelings toward the Romans. Philosopher Robert C. Solomon wrote extensively on the emotion of resentment and its negative effects on those who experience it. Solomon describes resentment as the means by which man clings to his self-respect, and as humanity at its lowest ebb.
The Alcoholics Anonymous organization cites resentment as the number one offender, and one of the greatest threats to an alcoholic. Several of the Twelve Steps of AA involve identifying and dealing with resentment as part of the path toward recovery, including acknowledging one's own role in resentment and praying for the person resented.
Resentment can also play a role in racial and ethnic conflicts, both in the United States and abroad. Resentment is cited as having infected the structure of social value, and is thus a regular catalyst in conflicts sparked by inequality. It can also be one of the emotions experienced during class conflict, particularly by the oppressed social class.