The behavior of lying in a person can be occasional, periodic or constant. It may be situational, habitual or compulsive.
Lying is common with Narcissists along with not caring about the impacts of that lying on others. Some Narcissists are pathological liars.
The Pathological or Psychopathic Liar can be most dangerous to others and themselves. An individual with this condition lies with no reservation, about things large and small, including the most inconsequential things where there is no apparent benefit for them to do so. They lie as a matter of routine, a way of life, even when they know it will hurt loved ones and hurt themselves. They sometimes also believe their own lies, enabling them to sound and look innocent and convincing with the victims of their lies.