1. it prevents discomfort
2. it leads to some economy of time and effort
   

Ego Defense Mechanisms include:

Acting Out:

The individual deals with emotional conflict or internal or external stressors by actions rather than reflections or feelings.  This definition is broader than the original concept of the acting out of transference feelings or wishes during psychotherapy and is intended to include behavior arising both within and outside the transference relationship.  Defensive acting out is not synonymous with "bad behavior" because it requires evidence that the behavior is related to emotional conflicts.

Affiliation: 

The individual deals with emotional conflict or internal or external stressors by turning to others for help or support.  This involves sharing problems with others but does not imply trying to make someone else responsible for them.

Aim inhibition:

Placing a limitation upon instinctual demands; accepting partial or modified fulfillment of desires.  Examples:  (1) a person is conscious of sexual desire but if finding it frustrating, "decides" that all that is really wanted in the relationship is companionship.  (2) a student who originally wanted to be a physician decides to become a physician's assistant.

Aim inhibition, like the other mechanisms, is neither healthful nor pathological, desirable nor undesirable, in itself.  It may be better to have half a loaf than no bread, but an unnecessary aim inhibition may rob one of otherwise attainable satisfactions.

Note that the first example could include the mechanism of displacement, and the second, rationalization.  Up to a point, mutual idealization can make for a happy relationship; however, unrealistic expectations of another person based upon this mechanism can lead to serious disappointment.

Altruism: 

The individual deals with emotional conflict or internal or external stressors by dedication to meeting the needs of others.  Unlike the self-sacrifice sometimes characteristic of reaction formation, the individual receives gratification either vicariously or from the response of others. 

Anticipation: 

The individual deals with emotional conflict or internal or external stressors by experiencing emotional reactions in advance of, or anticipating consequences of, possible future events and considering realistic, alternative responses or solutions.

Autistic Fantasy:

The individual deals with emotional conflict or internal or external stressors by excessive daydreaming as a substitute for human relationships, more effective action, or problem solving.

Avoidance:

A defense mechanism consisting of refusal to encounter situations, objects, or activities because they represent unconscious sexual or aggressive impulses and/or punishment for those impulses; avoidance, according to the dynamic theory, is a major defense mechanism in phobias.

Compensation: 

Encountering failure or frustration in some sphere of activity, one overemphasizes another.  The term is also applied to the process of over-correcting for a handicap or limitation.  Examples:  (1) a physically unattractive adolescent becomes an expert dancer.  (2) a youth with residual muscle damage from poliomyelitis becomes an athlete.  (3) Demosthenes.

Conversion: 

Conflicts are presented by physical symptoms involving portions of the body innervated by sensory or motor nerves.  This mechanism and somatization are the only ones that are always pathological.  Examples:  a man's arm becomes paralyzed after impulses to strike another  (2) regular heavy drinking limited to weekends; (3) long periods of sobriety interspersed with binges of daily heavy drinking lasting for weeks or months.

Deflection: 

Also detected when the individual is in group therapy and consists of redirecting attention to another group member.

Denial: 

Failing to recognize obvious implications or consequences of a thought, act, or situation.  Examples: (1) a person having an extramarital affair gives no thought to the possibility of pregnancy. (2) persons living near a volcano disregard the dangers involved. (3) a disabled person plans to return to former activities without planning a realistic program of rehabilitation. 

Devaluation: 

The individual deals with emotional conflict or internal or external stressors by attributing exaggerated negative qualities to self or others.

Displacement: 

A change in the object by which an instinctual drive is to be satisfied; shifting the emotional component from one object or idea to another.  Examples: (1) a woman is abandoned by her fiance’; she quickly finds another man about whom she develops the same feelings; (2) a salesman is angered by his superior but suppresses his anger; later, on return to his home, he punishes one of his children for misbehavior that would usually be tolerated or ignored.

Displacements are often quite satisfactory and workable mechanisms; if one cannot have steak, it is comforting to like hamburger equally well.  As the March Hare observed, "I like what I have is the same as I have what I like." However, the example of displaced anger illustrates a situation which, if often repeated, could cause serious complications in the person’s life.  Conscious acceptance of a substitute with full recognition that it is a substitute for something one wants is an analog of displacement.

Dissociation:

Splitting-off a group of thoughts or activities from the main portion of consciousness; compartmentalization. Example: a politician works vigorously for integrity in government, but at the same time engages in a business venture involving a conflict of interest without being consciously hypocritical and seeing no connection between the two activities. 

Some dissociation is helpful in keeping one portion of one's life from interfering with another (e.g., not bringing problems home from the office).  However, dissociation is responsible for some symptoms of mental illness; it occurs in "hysteria" (certain somatoform and dissociative disorders) and schizophrenia, The dissociation of hysteria involves a large segment of the consciousness while that in schizophrenia is of numerous small portions.  The apparent splitting of affect from content often noted in schizophrenia is usually spoken of as dissociation of affect, though isolation might be a better term. 

Fixation: 

The cessation of the process of development of the personality at a stage short of complete and uniform mature independence is known as fixation.

Help-Rejecting Complaining: 

The individual deals with emotional conflict or internal or external stressors by complaining or making repetitious requests for help that disguise covert feelings or hostility or reproach toward others, which are then expressed by rejecting the suggestions, advice, or help that others offer.  The complaints or requests may involve physical or psychological symptoms or life problems.

Humor:

The individual deals with emotional conflict or external stressors by emphasizing the amusing or ironic aspects of the conflict or stressors.

 Idealization:  

Overestimation of the desirable qualities and underestimation of the limitations of a desired object.  Examples: (1) a lover speaks in glowing terms of the beauty and intelligence of an average-looking woman who is not very bright.  (2) a purchaser, having finally decided between two items, expounds upon the advantages of the one chosen.

Identification:

Similar to introjection, but of less intensity and completeness. The unconscious modeling of one's self upon another person.  One may also identify with values and attitudes of a group.  Examples: (1) without being aware that he is copying his teacher, a resident physician assumes a similar mode of dress and manner with patients. (2) a school girl wants her mother to buy her the same kind of shoes her classmates are wearing; she angrily rejects the idea that she is trying to be like the other girls and insists that the shoes are truly the best available and are the style she has always wanted.  Conscious analogs of identification are intentional imitation of others and volitional efforts to conform to a group.

Incorporation: 

The assimilation of the object into one's own ego and/or superego.  This is one of the earliest mechanisms utilized.  The parent becomes almost literally a part of the child.  Parental values, preferences, and attitudes are acquired.

Intellectualization: 

The individual deals with emotional conflict or internal or external stressors by the excessive use of abstract thinking or the making of generalizations to control or minimize disturbing feelings. 

Introjection: 

The process of assimilation of the picture of an object (as the individual conceives the object to be).  For example, when a person becomes depressed due to the loss of a loved one, his feelings are directed to the mental image he possesses of the loved one.

Isolation:

The splitting-off of the emotional components from a thought.  Example: a medical student dissects a cadaver without being disturbed by thoughts of death.  Isolation may be temporary (affect postponement).  Example: a bank teller appears calm and cool while frustrating a robbery but afterward is tearful and tremulous.

The mechanism of isolation is commonly over utilized by obsessive compulsives.

Omnipotence: 

The individual deals with emotional conflict or internal or external stressors by feeling or acting as if he or she possesses special powers or abilities and is superior to others.

Passive Aggression: 

The individual deals with emotional conflict or internal or external stressors by indirectly and unassertively expressing aggression toward others.  There is a facade of overt compliance masking covert resistance, resentment, or hostility.  Passive aggression often occurs in response to demands for independent action or performance or the lack of gratification of dependent wishes but may be adaptive for individuals in subordinate positions who have no other way to express assertiveness more avertly.

Projection:

Attributing one's thoughts or impulses to another person.  In common use, this is limited to unacceptable or undesirable impulses.  Examples: (1) a man, unable to accept that he has competitive or hostile feelings about an acquaintance, says, “He doesn’t like me.” (2) a woman, denying to herself that she has sexual feelings about a co-worker, accuses him, without basis, of flirt and described him as a “wolf.” 

This defense mechanism is commonly over utilized by the paranoid.

A broader definition of projection includes certain operations that allow for empathy and understanding of others.  Recognition that another person is lonely or sad may be based not upon having seen other examples of loneliness or sadness and learning the outward manifestations but upon having experienced the feelings and recognizing automatically that another person’s situation would evoke them. [projective identification]

Projective Identification: 

As in projection, the individual deals with emotional conflict or internal or external stressors by falsely attributing to another his or her own unacceptable feelings, impulses, or thoughts.  Unlike simple projection, the individual does not fully disavow what is projected.  Instead, the individual remains aware of his or her own affects or impulses but mis-attributes them as justifiable reactions to the other person.  Not infrequently, the individual induces the very feelings in others that were first mistakenly believed to be there, making it difficult to clarify who did what to whom first. [projection]

Rationalization:

Offering a socially acceptable and apparently more or less logical explanation for an act or decision actually produced by unconscious impulses.  The person rationalizing is not intentionally inventing a story to fool someone else, but instead is misleading self as well as the listener.  Examples: (1) a man buys a new car, having convinced himself that his older car won't make it through the winter. (2) a woman with a closet full of dresses buys a new one because she doesn't have anything to wear.

Reaction Formation: 

Going to the opposite extreme; overcompensation for unacceptable impulses.Examples: (1) a man violently dislikes an employee; without being aware of doing so, he "bends overbackwards" to not criticize the employee and gives him special privileges and advances. (2) a person with strong antisocial impulses leads a crusade against vice. (3) a married woman who is disturbed by feeling attracted to one of her husband's friends treats him rudely.

Intentional efforts to compensate for conscious dislikes and prejudices are sometimes analogous to this mechanism.

Regression: 

By another anxiety-evading mechanism known as regression, the personality may suffer a loss of some of the development already attained and may revert to a lower level of adaptation and expression.

Repression: 

The involuntary exclusion of a painful or conflictual thought, impulse, or memory from awareness.  This is the primary ego defense mechanism; others reinforce it.

Resistance: 

This defense mechanism produces a deep-seated opposition to the bringing of repressed (unconscious) data to awareness.  Through its operation, the individual seeks to avoid memories or insights which would arouse anxiety.

Restitution:

The mechanism of relieving the mind of a load of guilt by making up or reparation (paying up with interest).

Self-Assertion:

The individual deals with emotional conflict or stressors by expressing his or her feelings and thoughts directly in a way that is not coercive or manipulative.

Somatization:

Conflicts are represented by physical symptoms involving parts of the body innervated by the sympathetic and parasympathetic system.  Example: a highly competitive and aggressive person, whose life situation requires that such behavior be restricted, develops hypertension.

Splitting: 

This term is widely used today to explain the coexistence within the ego of contradictory states, representative of self and others, as well as attitudes to self and others; other individuals or the self is perceived as "All good or all bad.

Sublimation:

Attenuating the force of an instinctual drive by using the energy in other, usually constructive activities.  This definition implies acceptance of the Libido Theory; the examples do not require it.  Sublimation is often combined with other mechanisms, among them aim inhibition, displacement, and symbolization.  Examples: (1) a man who is dissatisfied with his sex life but who has not stepped out on his wife becomes very busy repairing his house while his wife is out of town.  Thus, he has no time for social activities. (2) a woman is forced to undertake a restrictive diet; she becomes interested in painting and does a number of still life pictures, most of which include fruit.

The conscious use of work or hobbies to divert one’s thoughts from a problem or from a rejected wish is an analog of this.  Sublimation is often a desirable mechanism.  However, the consequences may, in addition to preventing instinctual satisfaction, interfere with the person's life in other ways if disproportionate time, money, or effort is used in the activity.

Substitution: 

Through this defense mechanism, the individual secures alternative or substitutive gratification comparable to those that would have been employed had frustration not occurred.

Suppression:

Usually fisted as an ego defense mechanism but actually the conscious analog of repression; intentional exclusion of material from consciousness.  At times, suppression may lead to subsequent repression.  Examples: (1) a young man at work finds that he is letting thoughts about a date that evening interfere with his duties; he decides not to think about plans for the evening until he leaves work. (2) a student goes on vacation worried that she may be failing; she decides not to spoil her holiday by thinking of school. (3) a woman makes an embarrassing faux pas at a party; she makes an effort to forget all about it.

In the first example, suppression was probably a desirable mechanism since it permitted concentration on work and deferred dealing with plans for the evening until a more appropriate time.  In the second instance, suppression would have been undesirable if failing work could have been corrected during vacation or if a realistic appraisal of probable consequences of the school situation would have permitted battery planning.

Symbolization:

An object or act represents a complex group of objects and acts, some of which may be conflictual or unacceptable to the ego; objects or acts stand for a repressed desire.  Examples: (1) a soldier, when asked why he volunteered, he said, "To defend the flag." He rejects as irrelevant a question about the purpose of the war. (2) a boy asks for a girl's hand (in marriage).

As in the second illustration, symbolization is often combined with displacement. it is one of the mechanisms usually involved in phobias. [avoidance] [displacement]

Undoing:  

An act or communication which partially negates a previous one.  Examples: (1) two close friends have a violent argument; when they next meet, each act as if the disagreement had never occurred. (2) when asked to recommend a friend for a job, a man makes derogatory comments which prevent the friend's getting the position; a few days later, the man drops in to see his friend and brings him a small gift.

In a conscious analog of this, Napoleon made it a practice after reprimanding any officer to find some words of praise to say at their next meeting.