Man's interest is defined as that which benefits his life.
It is an evaluation of the facts of reality.
Since the nature of man's life has particular, objective requirements,
determining whether something promotes his life is a statement of fact.
One's interests should not be confused with one's desires.
A desire is that which you wish to achieve or acquire.
A desire can be subjective or irrational.
One's interests, though, are objective facts of reality.
They don't state what you want to achieve.
They state what you should achieve to promote your life.
A proper morality is based on man's self-interest.
It is based on what allows him to live and flourish.
Identification of his interests allows him to decide how to act, and what values
It is the measure of right and wrong.
(This page mirrored from Importance of Philosophy.com)