Becasue shit happens and sometimes you just gotta get out of it and being a liar works. For instance in dating when you have reached the point where you know it isn't working rather than hurting the other person by telling them the absolute truth you lie to various degrees telling them you have met someone else etc when in fact it just may not be true. Hence, the need to get out of situations is satisfied by fibbing. There are so many degrees of lying. You just can't tell the "whole truth and nothing but"...even in court people lie!!!