Depression, split personality, narcissism etc. are all symptoms of the coping with one's situation by oneself in a setting where they don't really understand what's going on or what will happen. So basically, when i see a narcissist, i just see a person whos been exposed to an experience where they had to find a way to cope and survive.
Well said, Skedaddle! My far less erudite explanation after years of tying to understand how people that I knew and still love could be so...dangerous...is that they've been terrorized, backed into a corner, and they are dealing with life like a person who is gasping for what feels like their last breath, reflexively doing anything they can to keep alive and not knowing how else to continue. On the outside it looks calculated, but after knowing some of these sufferers intimately (read "close family members") I believe that they really can't comprehend most of the harm they do and they can't reason on it as we would wish because of the strangling fear. To coin a phrase: "They know not what they do" even though it looks calculated. Put them in front of God on Judgement Day and they can honestly say they didn't do it, and He will accept it. (Don't jump all over me for using this terminology, I'm just trying to show how absolutely out of control and beyond help such people really are.)