Psychopaths feel no guilt or remorse for lying, stealing, or hurting others so they may lie any time it benefits them. Most psychopaths learn that there are penalties for lying stealing and violence so they generally avoid doing these things unless the benefit greatly outweighs the risk. Where most people are guided by their conscience and empathy psychopaths are only guided by their self-interests. Sociopaths have been hardened or conditioned to not feel guilt or remorse for their wrongful actions. Growing up in poverty they may feel no guilt steeling from those who would be little harmed by the loss or being a frequent victim of violence they may not feel empathy for people they hurt Lying can be a symptom of psychopaths and sociopaths. Then again a child often feels no remorse for claiming it is their birthday in order to get a cupcake.
People lie for many reasons. Ayn Rand was a philosopher who taught that truth is important above all else. It turns out that she lied about her own academic achievements and qualifications. You could argue that by inflating her own achievements she would attract more people to her cause of Objectivism and increase the amount of truthfulness in the world. Her lie could convince others to be more truthful so you could argue that her lying served the cause of truth but you could also argue that she was simply a big fat hypocrite.
The definition of "pathological" is "caused by disease." By definition pathological liars are mentally ill. However, the latest Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) has no entry for pathological liars so the mental health field has no diagnostic criteria for it. At least by conventional wisdom there is no such thing as a pathological liar and no distinct illness that produces lies.
so it's probably cause of low self esteem that makes girls or sometimes guys lie constantly?