People are being a bit hard on themselves here.
Narcissism is not something you truly understand until you meet someone who really is one at the far end of the spectrum. Until you spend weeks, months or even years trying to work out why they have had their empathy glands removed you just don't fully understand the 'narcissism' concept. We see narcissists like The Donald and think that is it, actually you need to be on the sharp end of it, in a relationship directly or once removed through family or work to fully understand how insidious it is.
Only when you have learned the importance of 'no contact' do you understand narcissism fully.
All of us have a few traits that the narcissist has however, it is the cluster of characteristics that matters. With the HN readership I expect a fair few people here have genuinely found themselves on teambuilding exercises etc. where they really are the 'brightest person in the room' and have had to step up to 'leadership' because otherwise nothing would get done. That could be a tickbox on your internal 'I must be a narcissist' list. It doesn't make you one though. A lot of boxes have to be ticked.
Furthermore, the true narcissist does not have the brain cells to identify what the condition is. They can even hear of the story of Narcissus and think it is an 'incredibly sweet story', one worth sharing with others. How little they know...
Interestingly teambuilding exercises can lead to moments of 'imposter syndrome'. For instance you might never do sports yet fluke it with 'beginners luck' to beat everyone else. This happened with my sister who can't drive. When she went go-karting with her petrol-head workmates she somehow won. On that day she felt quite the 'imposter' in collecting the prize, not believing it. She was 'quite full of herself', ego brimming, and with a few 'narcissist checkboxes' ticked that day. So there is a correlation.