I know I've said several times here that "it doesn't matter why a person behaves the way they do; if their behavior is unacceptable, that's all you need to know."
I can change.
It was just suggested to me that my AXH could possibly be diagnosed with NPD (by a mutual acquaintance who is a psychiatrist). I was pushing that away saying "being a jerk is not a mental disorder, it's a choice" and she said "whichever way you want to view it, learning about the disorder may help you have realistic expectations of him, and that will help you, right?"
And yes. She's right. I guess. About NPD or alcoholism or whatever. I guess it's like... it's better to understand once and for all that the hardware store doesn't carry bread rather than going back every six months to see if maybe they've updated their inventory...
I still stand by LTD's quote in my signature -- that unacceptable behavior is unacceptable -- but I can also understand the value of scouting out the merchandise of the hardware store so I can stop going there when I need a sandwich.