Knowing somebody was out of their mind when they slugged you does not keep a knot from rising up on your head. Knowing somebody did not give you the flu intentionally does not keep your fever down. And knowing that somebody is narcissistic does not keep you from hurting horribly because of their nastiness.
I think that everything we learn about narcissism EXPLAINS the behavior but it can in no way EXCUSE the behavior. We all have psychic wounds. And we all have choices. Learning about N helps you to see that it ISN'T YOU but that is not to say that you can ever be OK with THEM just because you understand N. They are destructive.
I believe there were reasons why Hitler turned out the way he did. But nothing nothing nothing can ever undo the mass destruction he left in his wake. Reasons why help us make sense of what happened to us. They do not help the pain.
I do however think that reasons why can help us make decisions about OUR behavior that will help the pain in the future. For example, this week I was having a pleasant conversation with my mother when she suddenly inserted a nasty and insulting comment. In years past, I knew that she was making me angry but couldn't pinpoint why (because she smiles and acts like she is being funny, and I swallowed her gaslighting attitude that I should not be hurt by such comments) ... and so I would blow up at her and then she would act all hurt and like she didn't understand what my problem was. Because of my understanding and clarity, I looked at her and said mildly, "Well, that wasn't a very nice thing to say." Which totally deflated her because it was talking to her like she is a child and mildly reprimanding her, and refusing to either act ugly myself (so that she could play the victim) or to ignore it (act like she wasn't trying to hurt me). She immediately started backpedaling, and it gave me some satisfaction.
I also think that understanding N helps us stay out of the booby traps, both in existing relationships and when we are making new ones.
But it doesn't help with the pain of what has already happened. I think processing ---- allowing ourselves to fully remember what happened to us, talking about it, journaling about it, creating works of art (music, collages, etc.), and making sense of it --- does help the pain. Processing helps us to put the N wounds into perspective inside the whole picture of our lives.