A pathological liar is someone who tells lies compulsively, often for no apparent reason. Maybe a friend tells you a detailed story about how they witnessed a car crash into a bank last night. They gain nothing from telling this elaborate lie, and it’s easy to debunk, but they make the claim regardless. Pathological lying without motivation in this way may be the result of a personality disorder. Whatever the cause, though, it can have a negative impact on the liar’s social life, creating relationship difficulties at home, work, or school, and even lead to legal problems.