I don't have borderline myself, but I have a good friend who has it, and have certainly seen others with it as well. I've heard that it is like a perpetual state of angst or lack of consistent inner definition. Some people strike or act out whenever they are without footing, so being like that all the time just gives more chances to do so, without any sort of balance. I'm not a psychologist or therapist, but I've heard a lot so maybe some things are good.
It seems like, cognitively, there are disruptions in forming and reconciling with a "self" in borderline. (It is hard to work on self worth if there isn't a self to value, or fill emptiness if there isn't some container to hold what is made.) But the definitions, judgments, and presence of others provides some sort of form to hold on to; something that is perceived. So some attach themselves to others, especially strongly self-defining people. Other people act out or make a caricature to get a strong reaction and definition from others.
I was hospitalized with depression, and I remember being in a DBT group where someone said they would openly seek being disliked just for that constant sense of something. Of course then they felt bad and guilty because they weren't sociopathic- they disliked hurting and antagonizing others all the time, but didn't know what to do or got caught up in their own feelings at the time. But he couldn't dislike in a way that was isolating- it had to weave into some level of acceptance from people to continue interaction. (I'll be honest, I was pretty out of it at the time and I don't remember all his reasonings, but the general format stuck with me. He was pretty vicious, and got removed a bunch for acting out. Which...well...) Sort of the format of making "that guy" as "who I am," at a more fundamental level than just acting a certain way or playing a character.
Another big part with self-reconciliation is the idealization/demonization of others, which seems to be in line with the difficulty in forming a whole idea of a person. Usually the term black-and-white thinking is used, where there is no gray zone of action. The traits and emotions demonstrated at a particular instant are the definition of that person, and borderline usually has overriding emotional responses that shade even this limited view. People are like idealized characters rather than full human beings, so any expression counter to that character is incredibly dissonant. That a person could express both kinds of traits is hard for borderline to work with, as they have difficulty both creating that container or overall narrative of a person, and reviewing that narrative without it being overwhelmingly emotionally reactive. Like perfectionism, but also stemming from difficulty in forming a level picture. (The example for reconciling usually is something like Einstein- he both was fantastically influential in science, and fairly adulterous, although not as bad as it can be made out.)
I've done an exercise in listing out good things about a friend/person or good things a person has done, and then on another day listing things you dislike, regardless of any person. Then, using relatively less reactive recent incident, combining that emotional experience with the good qualities and listing them together, or reviewing small things in a visible format. Not in the sense of adding a flaw to a character, but coming with both qualities. Building it manually. I saw some people be strikingly bothered by the exercise. The self-hatred was tough.
Narcissistic personality disorder I think has a separate self dysregulation in that there is a self that is constructed and, but one that is markedly idealistic and intolerable to any disturbance or deviation. An "actual self" is not handled. Other people may not even be perceived as having selves or are considered inherently less equal by lack of sharing this ideal self. People are characters or tools, even playthings, yet they also express the social framework that the narcissist cannot control, and wield an unusual power in this way. As such, perhaps controlling others also stabilizes more of the self.
It bugs me when people give examples of "borderline" people in relationships who might be narcissistic instead. If they've always shown self-aggrandizing all the time and rarely show compassion without some secondary benefit, it might be a bit different. Borderline involves that idealization half as well, and admiration doesn't seem like something that would be expressed by a narcissist, unless it was in a manipulative way. Hard call.
I'm glad to say that my friend is finally doing well after a long and destructive path (and a psychiatrist who said they didn't know what else to do with her), so I've seen that borderline can definitely be helped. I think she is on topiramate and abilify, or maybe topiramate and lamictal, and continuing a lot of therapy like DBT, mindfulness, and some self work. Really made a change.
tl;dr borderline is rough on many levels. You are a person, more than the current emotions, and more than self-hate. I wish those with it the best with finding treatment and understanding.
