In 1920, Sigmund Freud first elaborated on his structural model of the human psyche. According to this new theory, the mind is divided into 3 distinct parts. Humans are born with the Id which contains all our drives for pleasure and self interest. Soon after birth, the Ego is developed whose main focus is on interacting with reality and find ways to satisfy the Id's desires. Over the next few years, the Superego appears, which is all the rules inherited from our parents and society or the principles a person chooses.
Even if one does not subscribe to the idea of these divisions in the mind, there is still much to learn from this structure. In healthy people, according Freud, the ego successfully manages to balance to opposing forces: one's intentions (Id) and what one believes should be done (Superego). On one hand, giving in to a hedonistic lifestyle (too much Id) brings harm to one self and to others. On the other hand, an excessive sense of morality or other concerns (an authoritarian Superego) leads to a denial of one's needs and creates suffering. (Source 1).
Analysis does not set out to make pathological reactions impossible, but to give the patient's ego freedom to decide one way or another.
Freud's conjecture is a relatively recent example of balance in Western civilization that provides a clue of how to live a better life: people should examine whether they are attending sufficiently their wants or not. If so, they should also reflect about whether or not their choices regarding self-satisfaction are in line with their principles, whether the benefits outweigh the total costs or vice-versa, and if there are better ways to find gratification.
Observation: When in colloquial conversation a person is referred to as "Egocentric", in the Structural Model he or she would be describe as having a strong Id.
Source 1: http://allpsych.com/psychology101/ego.html (Accessed: October 14th, 2011)