I would like to qualify one of the above posts that refer collectively to personality disorders. I do not personally know anyone who has been diagnosed specifically with Narcissistic Personality Disorder.
However, I DO know people who fit the criterion and/or have been diagnosed with Borderline Personality Disorder. In a different thread, I assertively disagreed with a poster who stated as a fact that BPD can not be “cured”. I have since been in contact with one of the foremost professionals who specializes in BPD. She clarified, that often when people are describing a person with Borderline Personality Disorder, the person they are referring to ALSO has Narcissistic Personality Disorder. This detail may explain the difference of opinion and experience I have with Borderline Personality Disorder. People who fit the criterion can definitely recover, and overcome most if not all of the symptoms with a mixture of various approaches. It is very hard work, and every step is heroic. A person who is in the process of recovery deserves a lot of support, respect, and inclusion.
If they have co-existing Narcissistic Personality Disorder, I do not claim to know the dynamics, or how one might recover from that. As a frum Jew, I find it difficult to believe that something that is truly a personality disorder can not be improved upon with the proper approach. But we are using terminology that does not clearly describe biological realities. We are using terminology that was created by humans, to describe a particular group of behavioral symptoms. Only Hashem knows where a person’s nekudas habechira lies at any given time. Maybe for some people, the nisayon is just to recognize that there is something to fix. That recognition may be a tremedous avoda in itself! (meaning it will take a considerable amount of time and effort to just acknowledge that there is a problem). And maybe that is what Hashem wants from them.
Also, I would like to second the poster who explained that treating an emotional/mental health problem allows the person to get to a place where they can THEN learn mussar, and apply it. Ironically, the people that I have encountered who have worked very hard to overcome emotional dysregulation with therapy, are already practicing actual mussar concepts; they have challenged previous thoughts and behaviors, and systematically use particular skills to CHANGE their default responses.
However, had they gone directly to a mussar sefer, the effort would have likely backfired. The first thing they would experience is guilt, self-blame, hopelessness, and other non-productive emotions. Their issues would likely get worse, and the mussar would not be able to be internalized. Because the part of the person that can integrate mussar is not functioning properly! Professional intervention is indicated for healthy function to either resume, or possibly to begin for the first time.