I don't think there was ever a "point" where it all changed - I don't even think I've changed that much. I'm just more aware of my own inborn tendencies, so I can both use them to my advantage (like choosing a career where recognition is built in) and to spare others of my bullshit.
As for the how, someone once told me that you see God in someone else's eyes. Well, I definitely became more aware of my own toxic traits by studying people I cared about who I found annoying, manipulative and cold. It was just never enough for me to label them a narc to move on--and eventually I realized I was just like them, lol.