I'm not sure I know what makes them tick either. Especially the lying, but having a mental health issues background it does make you want to keep secrets. You never know how people are going to react when you tell them you are mentally ill. I know a lot of people hide their mental health status to protect themselves from ridicule or being looked down on. I'm sure other people think they have good reasons. I'm pretty upfront with people I know well but tend to keep my mental illness from those I only causally know.
Gayle