Well you're asking like 20 PhD level questions here so bear with me while I try to answer. Right now the question of "what to do with narcissism" is the therapy equivalent of asking 'what is gravity'. Really no one knows fully but we can measure it's effects (because we have statistics on things like rape, assault, crime, bigotry, racism, etc) and if I can sum up decades of amateur research I'd say it's at the root of most poor human behavior. So trying to wrap our minds around this beast is important and incredibly complicated.

>Why is it only true to "an extent"? It's literally what it is. /Surely it is a spectrum

The 'to an extant' part is me referencing that it is indeed a spectrum.

>It's entirely an interpretation of a human being based on the words of another human being.

I think you're being unfair to the scale of the problem. I'm going to rant here but stick with me--if you want to semiotically break it down, 'narcissism', as defined by the inability to fully understand that another person or group of people, are indeed people, is probably responsible for most of humanity's issues today and throughout history. Racism? It's really just a type of narcissism. Pedophilia? Really just narcissism. Rape? Narcissism. And to complicate things, it's on a *spectrum of intensity* as well. A pedophile is not the same as an ephebophile, etc. Emotional abuse is a little different from physical abuse. But what all of these things have in common is that the narcissist violently breaks a boundary (emotionally, physically, financially, socially) because they don't really see another type of person as a person, just an object to be acted upon for gain, power, or entertainment.

So yeah, it's an interpretation coming from other humans, from outside, but we do have enough data on these behaviors (and narcissism research if anything is actually increasing) to see that they do hold up across many different types of pathologies. A wife abuser has a lot of similarities to a pedophile who has a lot of similarities to a serial rapist who is similar to a dirty cop...on and on.

>Sure certain behaviors of patterns could be destructive. But I don't see any practical use of categorizing and labeling a complex set of behaviors into "NPD" or "not NPD". Is there a clear cut off line of what is NPD and what isn't?

Well it's because it does help 'on the ground' in terms of therapy. For some background I have had a life-long interest in abnormal psychology and I have a side-gig where I run virtual workshops for a therapy institute. I'm not a professional but I get to sit in on a lot of workshops and hear therapists talking between each other and doing trainings.

>Also its possible one person with the same exact behavioral patterns as another could be widly successful in a different environment. Does that mean one has NPD and the other does not?

Your question is not disimilar to one I heard in a workshop with Dr. Laila Ramani who is an NPD expert. Her answer is that it's complicated. You have to hold what it means for something to be a disorder (negatively affecting a subjects life AND/OR the lives of those around them) ALONG WITH the idea that the disorder could be the comorbid expression of something else. ALONG WITH the idea that if it truly is NPD it just may not be treatable.

So for example, if someone walks into your clinic expressing depression and narcissistic traits that are both DISORDERING their life, when you treat them, you treat them for the depression and see what's left. It's a subtractive process. If the narcissistic behaviors also disappear, then what was happening was that their depression was causing them to 'turn inward' and become more and more 'narcissistic' in the sense that it's hard to care about others or yourself when you're in such an emotional hole. But as the depression goes away so does that poor behavior whether it's harming others or self.

BUT, and this is the fucked up part, if you treat the depression but the patient comes in and they're like "My job sucks, my partner is a worm, blah blah" then...that person actually kinda-sorta still does have narcissistic traits, it's just not *disordering* at the moment. If their partner is fully codependent, that partner will ignore or participant in their behavior. If their job is on wallstreet, it's likely rewarding their Machiavellianism.

So you've treated the depression...but now you have a happy narcissist. At the moment.

But there's always a high chance with these people that they will indeed hit some form of rock bottom, even if they do seem to 'get away with it' on the surface.

Dr. Ramani ended answering that question with a personal anecdote about a patient exactly like this. They just flat out had NPD, were basically successful externally, but kept burning through personal relationships.

They eventually self-isolated and was doing ok. Lonely and whatnot but OK. And Dr. Ramani was sad about that but also realized that may just be the actual solution.

But just personally, look we have nuclear weapons and all kinds of world-ending technologies coming down the pipe. If you have kids you'll realize these are not traits we can keep passing into the future unchecked.