As clinical psychologist Dr. Joseph Burgo states in his book The Narcissist You Know:
“Although the APA sets forth nine potential criteria for Narcissistic Personality Disorder…. those nine actually boil down to two: an inflated sense of self-importance and a lack of empathy for other people; the remaining features are by-products that naturally follow from them.”
1) an inflated sense of self-importance
2) a lack of empathy for other people
Bingo! There it is, in a nutshell.