Narcissism was clinically defined by Sigmund Freud and was named for the character in Greek mythology named Narcissus. He was unable to love anyone else, instead falling in love with the reflection he saw in the water--himself. Narcissism is much more significant than simple greed or ego-centrism, as it permeates the person's mind as well as his way of life.
Those with this condition may also suffer from what is termed "narcissistic withdrawal."
Children suffering from narcissistic withdrawal turn away from parents and other caregivers under the misguided (and quite mistaken) notion that they can satisfy their own essential needs. This is a demonstration of omnipotent narcissism, a belief that one is all-powerful and capable of doing or providing anything that must be done or is needed.
Adults suffering from the same condition withdraw from all long-term relationships. Even in their more short-term relationships, they withhold or withdraw themselves from the other(s) (through such techniques as the familiar "silent treatment") in order to prevent those relationships from becoming long-term.
While there are obviously many problems associated with narcissistic withdrawal, some psychologists see this as a positive behavior for those suffering from narcissism. This withdrawal may, in fact, help the narcissist adapt to his reality.
[T]here is an aspect of withdrawal that is healthy, considering that it might be "helpful to think of withdrawal as a condition in which the person concerned (child or adult) holds a regressed part of the self and nurses it, at the expense of external relationships...."
In other words, narcissistic withdrawal may help the sufferer heal his inner wounds, though he must sacrifice his relationships to do so.
A more extreme version of this condition is called "schizoid withdrawal," and it is characterized by the complete extermination of all relationships.
This can also be viewed in children, which when the case, it is characterized from turning away parental figures and believing in a fantasy that needs can be satisfied by the person alone. If adults are having this issue, it would be used in relationships more where they would tend to draw away from others with the 'silent treatment' to make sure the relationship doesn't drag on or become long-term.