Refusing to attend your best friend's wedding because you don't feel like meeting that many people, and shouting from the rooftop that doing drugs is bad, are not narcissism. It's called having preferences.
Telling people that they have the obligation to fight for the rights of marginalized people, and people need to stop what they are doing right now and go out on the street to protest for peace, are narcissism.
Because narcissism means treating others as extensions of one's self, not how well they phrase their demands, or how virtuous their ideology is.
I take the whole “The genuine poet is an intuitive psychologist” very seriously. Because I actually wanted to throw up multiple times when I started learning writing and was aware of the social pressure to say things that didn't feel right. Most of my analysis comes from my writing process, and not from reading textbook theories. I barely read any books.
But people who only read books and don't do much daily practice frequently miss subtle signs of narcissism. Outside of writing, just thinking about stuff a lot helps too.