Comparison is the thief of joy.

-Theodore Roosevelt

Humans use social comparison to determine our social and personal worth. We do this by consciously and subconsciously continually evaluating our attractiveness, wealth, intelligence, occupation, status, success, etc., against others. 

American social psychologist Leon Festinger is credited with the social comparison theory. He proposed that people constantly seek honest self-evaluations and compare themselves to others to gain a better sense of themselves and where they are in their lives.

In these situations, people typically compare themselves to someone who has at least one major characteristic they have in common. We begin applying social comparisons at a very early age to help construct our sense of identity.

There are two types of comparisons: upward and downward.