We all know someone who is a little bit narcissistic, but what differentiates that from having a full on personality disorder? NPD is a pervasive pattern of grandiosity. There is a highly elevated sense of self-importance, they're different and unique, they deserve more than what they have becuase they're uniquely qualified and special. As friends, if they don't feel good you can't feel good. NPD makes it hard to keep friendships due to interpersonal exploitation. Using others for their own gain and putting people down who don't make them feel good about themselves. Their self-esteem is very fragile and they lack empathy for others. They have very little time discussing or attending to the needs of others while expecting people to be happy for them or help with their issues. They typically have an intolerance for criticism and defeat.
Working or loving someone with NPD can be exhausting and damaging. Reaching out for help for yourself first is important, lots of people with NPD do not realize. Treatment is possible, but as with a lot of things, the road to recovery and self understanding is a long and bumpy one.