Psychologist Robert Feldman cites self-esteem as one of the biggest culprits in our lying ways: "We find that as soon as people feel that their self-esteem is threatened, they immediately begin to lie at higher levels."
Feldman believes many lies are simply for the purpose of maintaining social contacts by avoiding insults or discord.
Small lies that avoid conflict are probably the most common sort of lie...and avoiding conflict is a top motivator for deception.