People lie because they feel like they need to. Sometimes this is justified. A classic example is the man who hid Jews under his floorboard in "Inglorious Bastards.” When the Nazi came looking for Jews, most people would agree it’s morally correct to lie in order to save life. Lying isn’t always a bad thing.
Conversely, there are liars like Casey Anthony. Some people only believe what they choose to believe and become so good at acting because they cannot distinguish the fabricated roles from reality. It’s unfortunate.
Thanks for the question,