The common sense idea of these disorders is that the narcissist is self-absorbed, and controlling and the borderline is insecure, and unstable.
Healthy and secure separation from parents or caregivers means coming to see oneself as an independent being.It has only been in my lifetime that this understanding of problems related to childhood disruptions in attachment and individuation have come to be seen as in fact quite treatable.And the treatment technique for borderline personality disorder called Dialectical Behavior Therapy is well established and heavily evidence based. Sees self and others alternatively as all-good and all-bad. People with borderline personality disorder has a persuasive pattern of instability in interpersonal relationships. Narcissistic personality disorder: Egotistical, arrogant, grandiose, insouciant.The crucial time for this phase of development is thought to be around 18 months to 3 years (which coincides, quite logically, with the terrible twos).Both narcissists and borderlines grow up needing to define themselves in terms of other people in order to feel viable.
This is the disgraced tycoon or the politician with a secret fetish.