It means that the person will lie, cheat and more than likely steal from you. You can't trust a word they say and they have many affairs, gaslight you and in the end leave you when you either wake up to what trash they are or you are left weak, broke and offer less that the next sucker they are working on in the background. Someone just like Sandra Leske.
Good parenting at an early age is crucial to the prevention of NPD according to some psychologists, others say that they are born that way. Who knows.
Exposing a narcissist to their current associates often backfires because of the narcissist's ability to manipulate and charm others. Their associates may be loyal to the narcissist and believe their side of the story rather than yours, leading them to think you are the one with the problem. It is usually more effective to focus on setting healthy boundaries and protecting yourself from the narcissist's behavior.