Existential Psychology is a contemporary approach that was popularized by Dr. Irvin Yalom. Existential psychology is based upon the premise that all psychological inquiries can be reduced to man's struggle with the essential facts of life: the certainty of death, the certainty of loss, and the sense of utter separateness from fellow man. Existential psychology views all human behavior as an attempt to deal with these facts. These attempts are called defenses. Some defenses (i.e. having offspring as a way of extending one's mortality) are considered healthy. Others (i.e. overeating to escape from one's sense of loss) are considered unhealthy. Existential psychologists try to help people replace unhealthy defenses with healthy ones.
Personality psychology views human behavior as the result of nuanced interaction between an individual's mental, emotional, and biochemical constitution. Personality psychologists understand behavior to be the result of these various factors. They may employ terms such as "narcissist," "overachiever," or "passive-aggressive personality" when describing an individual's behavior patterns. Personality psychologist are also interested in the social context of behavior and may study birth-order, religion, or culture as an aspect of personality.