Psychology, Diagnoses, and NPD vs. BPD

It may help conceptually to think of "NPD" as more ego, power, and arrogance about intellect, ability, entitlement, and privilege, compared to thinking of "BPD" as more about emotion, social interaction, feelings about fairness and righteousness, and resentment. They can be seen in the same person, however BPD (borderline personality disorder) was "discovered" as a cluster of behaviors that seemed to show up together, hence the name "borderline"... the origin of the behaviors was not understood, it kind of seemed like this or that, like it was in between, so (for real) it was called "borderline", as in being on the "borderline" between different apparent disorders or illnesses.

Psychiatry and psychology are practiced theoretically. If a person's "condition" has not been tested medically and found to have a specific biological origin, then it's not being treated as a biological health problem. It's being viewed and treated theoretically as a psychological issue. In other words, not medical and organic, but more abstract.

As one psychiatric nurse in a well-known psychiatric hospital said,
"If you went to six different psychiatrists here you would probably get six different diagnoses."

Psychiatric diagnoses are not engraved in stone, they are theoretical. Neurological conditions are investigated biologically, as in looking at the brain to see if it there is disease or injury. If there has not been given a neurological diagnosis, then the client is being diagnosed and treated theoretically. It LOOKS LIKE bipolar, so here's a prescription, let's see if it works, and how well. It LOOKS LIKE BPD, so here's a prescription, let's see if it works.
It LOOKS LIKE depression. It LOOKS LIKE schizophrenia. It shows the signs and symptoms of what we have been saying is this certain condition, so we'll treat it as such.
When a person is given a psychiatric diagnosis, it's not the same as a medical diagnosis. And further, the amount of medical misdiagnoses that occur should give an indication about how it can occur, and how often, with a psychiatric diagnosis. These things need to be carried out with humility and the understanding that it's theoretical (on the medical practitioner's part AND the patient's part, and also the people in the patient's life), until it's proven scientifically with accuracy. Like a blood test for a specific chemical, for example.

All health care practitioners are human beings who have limited amounts of information, and limited ways of obtaining information. They are not gods, and should not be expected to perform like gods, to know everything, to be perfect like a god. Expectations like that (from both people as patients and individuals in the medical community) cause a lot more problems than solutions. On one side of the coin, a practitioner who sees themselves as above others is prone to make errors in judgment about colleagues, patients, and medical science or theory, because arrogance does not double-check itself. On the other side of this coin, a patient can have confidence in one's health care practitioner, because they have seen their ability for themselves, without expecting them to be perfect and omnipotent.