There are a number of reasons that people lie. The first is fear. This is the most common reason that people may lie, and they are taking shelter from a perceived punishment. It may be because they know they have done something wrong a single time, in which case it is not compulsive lying.
But if someone is always in fear of being punished, then lying may become a habit, which is a second reason for lying. In this case, it may become compulsive lying, which is lying by reflex. Even when confronted by the truth, they insist the lie is the truth in this case. A third case is learning to lie through modeling. When a people see others lie, especially when they get away with it, they may become more prone to lying. Finally, people lie because they feel if they tell the truth they won’t get what they want. Thus, out of the main reasons for lying, only lying by habit can truly be called “compulsive lying” or “pathological lying”.
Increased lying has been seen with a number of psychiatric diagnoses such as ADHD and Bipolar Disorder. With ADHD people will often say “I don’t know why I did that”, and when confronted about why they lied, their answer will be the same. ADHD children also display impulsivity, and they may lie implusively. Bipolar Disorder can be associated with low serotonin levels, which has been implicated in impulsivity, which, as indicated before, makes a person more prone to lie.
Pathological lying, though, can be thought of as being associated with a select few psychiatric diagnoses, which normally have their onset during adolescence. Namely, these are Conduct Disorder and Antisocial Personality Disorder. In conduct disorder, it is common to seelying, conning people and other forms of deceit. In Antisocial Personality Disorder, there is a pervasive pattern of disregard or the rights of others, and with this, the person with this disorder will often lie to get what they wish – usually money, sex or power.