DEFENSE MECHANISMS
Although defense mechanisms are normal and universally used, when carried to an extreme they lead to compulsive, repetitive, and neurotic behavior. Because we must expend psychic energy to establish and maintain defense mechanisms, the more defensive we are the less psychic energy we have left to satisfy id impulses. This, of course, is precisely the ego's purpose in establishing defense mechanisms - to avoid dealing directly with instinctual demands and to defent itself against the anxietyt that accompanies them.
The principal defense mechanisms identified by Freud include repression, undoing, isolation, reaction formation, displacement, fixation, regression, projection, introjection, and sublimation.
(I'll be tackling Undoing and Isolation but will give a quick background for repression)
REPRESSION
The most basic defense mechanism, because it is involved in each of the others, is repression. Whenever the ego is threatened by undesirable id impulses, it p[rotects itself by reperessing those impulses; that is, it forces threatening feelings into the unconscious. In many cases the repression is then perpetuated for a lifetime.
Repressed drives may also find an outlet in dreams, slips of the tongue, or one of the other defense mechanisms.
UNDOING AND ISOLATION:
When repression would block out too much reality, people may rely on undoing and isolation to derfend against anxiety. Undoing and isolation are important variations of repression and are distinguished from repression by their close association with repetitive and ceremonial acts and with persistent and recurrent thoughts.
UNDOING is a type of repression in which the ego attempts to do away with unpleasnt experiences and their consequences. It is like negative magic in that ideas or events are made to disappear, erased through compulsive ceremonial bahaviors. A classical example of undoing is found in Shakespeare's account of Lady Macbeth as she ceremonially rubs her hands in an effort to wash away guilt of Duncan's murder. By cleansing her hands, she hopes to undo the part she played in the king's death. Her attempts of repressing guilt, however, are not completely successful. When undoing is complete, the person would have no conscious memory of the actions that produced the guilt.
Undoing shades into normal behavior when it takes the form of repeatedlyy making the same mistakes, habitually and rituallistically wasting time, or compulsively looking in the same place for a "lost" possession. In mild undoing, a person looks away from an unpleasant experience as if it never happened.
ISOLATION
A closely related defense mechanism is isolation. With isolation the ego attempts to isolate the experience by using obssessive thoughts to block out any affect that immediately follows the experience. By blocking out the affect, a person severs the association between an unpleasant event and subsequent experiences. The undesirable event thus isolated and cannot be recalled by ordinary thought processes. Whereas undoing produces compulsions and ceremonial bahaviors, isolation leads to obsessive thoughts and recurrent ideas.
Freud believed that a degree of isolation is common in normal behavior when the ego functions to keep certain thoughts separate, thus breaking the chain of associations between current thoughts and the anxiety-arousing thoughts that accompanied the original unpleasant bahavior.
Book:
Theories of Personality (5th Ed.)
Jess Feist and George J. Feist
McGraw Hill, 2003