Narcissists are, by definition, incapable of seeing themselves honestly, as they come across to others. They have moments of deep insight into others - and even occasionally into themselves - but they can't integrate any accountability of vulnerability into their self-image on a consistent, ongoing basis. They live life as human castles, with elaborate emotional moats guarding them at all times.
Narcissists will break your heart and shatter it into a million little pieces. Imagine being someone who could harm another person that way. That would be a lot to carry around - unless you're a narcissist, in which case you're eternally faultless.
A small percentage of the population is believed to have the full-blown personality disorder, say, 2-4 percent. But the few who exist are plenty, right?