“We don’t see things as they are,” says a proverb. “We see things as we are.”
Dawes (1990) proposes that this false consensus may occur because we generalize from a limited sample, which prominently includes ourselves. Lacking other information, why not “project” ourselves; why not impute our own knowledge to others and use our responses as a clue to their likely responses?
Most people are in the majority; so when people assume they are in the majority they are usually right.
Also, we’re more likely to spend time with people who share our attitudes and behaviors and, consequently, to judge the world from the people we know.
On matters of ability or when we behave well or successfully, however, a false uniqueness effect more often occurs (Goethals & others, 1991). We serve our selfimage by seeing our talents and moral behaviors as relatively unusual. For example, those who use marijuana but use seat belts will overestimate (false consensus) the number of other marijuana users and underestimate (false uniqueness) the number of other seat belt users (Suls & others, 1988). Thus, we may see our failings as relatively normal and our virtues as relatively exceptional.
To sum up, self-serving bias appears as self-serving attributions, self-congratulatory comparisons, illusory optimism, and false consensus for one’s failings.
from: Social Psychology - David G. Myers