People with personality disorders, such as Narcissism or Borderline among others, often do not realize that they have a disorder at all because their way of thinking and behaving seems natural to them. They may blame others for challenges and cannot see that they are the common denominator in their problems. Unable to understand that they are causing the dysfunction, they are not very motivated to work on it.
Instead, it is often the loved ones who reach out for help. Personality disorders cause a severe disruption in how relational information is processed, so it is the people around them who suffer. When only one person is doing the work, the relationship cannot mend.
The partner of someone with a personality disorder may recognize a profound lack of resolution in the relationship. Couples may have repeat arguments, one partner thinks that they are reaching an understanding, and then later realize that no change has actually occurred. That partner may also be frequently blamed for the issues that the personality disordered person is causing (a dynamic we call “Right Room, Wrong Person”). For example, the personality disordered person may be yelling and asking why their partner is being so rude, when, in fact, they are the one being rude. Some level of this dynamic may happen in every relationship, but the frequency and duration sets apart those with a personality disorder.