Sam Vaknin argues that borderline personality disorder (BPD) is a mirror image of narcissistic personality disorder (NPD): whereas narcissists defend against the threat of others’ presence by internalizing and “snapshotting” them, borderlines defend against absence by merging and outsourcing psychological functions to others. Although BPD and NPD can appear behaviorally similar—withdrawal, devaluation, cycles of idealization and discard, and comorbidity with avoidant and other personality disorders—their underlying dynamics differ (narcissists seek separation from external objects into internal introjects; borderlines fear abandonment and engulfment, leading to approach-avoidance repetition compulsion). Vaknin also distinguishes avoidant personality disorder as a related but narrower condition characterized mainly by chronic avoidance driven by rejection sensitivity and low self-worth, and illustrates these differences with clinical examples. Borderline: Narcissist’s Mirror (and Avoidant Personality Disorder)