Antisocial behavior. Pathological liars lie b/c they have never developed remorse for their behaviors and have perceived that they have obtained advantages in life due to lying. Lying may have been a way to cope or adapt to an early pathological family situation or other life situation. In the end, it can be harmful to the person and others. He or she must gain insight into the consequences of his or her actions.
There are different. types: Sociopathic Personality disorder (SPD), compulsive lying (CL), Narcissistic Personality disorder (NPD), etc. With CL, lying begins early on for many reasons and it can become routine, second nature, as with many behaviors. With SPD, NPD, the reasons for lying are far more complex, from childhood- for personal gain, avoidance of legal/social penalty, or linked to alleviation of envy, etc.