Borderline personality disorder is a disorder that affects 2% of the population. This disorder primarily of three features: "an unstable sense of self, impulsive thoughts and behaviors, and sudden shifts in mood." This means that there is a lot of unexpected anger, sadness, and irritability often provoked by a fear of abandonment.
One theory is that of Drs. Peter Fonagy and Anthony Bateman who that children can loose their ability to mentalize if as a child they are not taught the appropriate emotional reactions to situation, because the caregiver cannot give enough attention to the child to teach these responses. This means that in later life the person looses the ability to grasp the reality of situations. He or she will create a warped reality based of insecurity, anger, etc. and does not grasp that this reality is warped.
BPD's features of impulsivity and anger lead to dangerous behaviors, often self mulitation and suicide.
Uncertain and confusing family relationships were found among those with BPD. The ongoing emotional pain of BPD is felt most strongly in interpersonal relationships. Those close to one with BPD must reenforce the relationship without reenforcing the negative behaviors
In people with this disorder is has been shown that their brain activity fires only when receiving. In a normal person it fires when both receiving and giving. This strongly implies that they cannot grasp the consquences their actions have on others.