This thought came to me suddenly about two hours ago.
An example of self interest is this. If a tornado's coming, you worry about you, your loved ones, and your stuff.
An example of narcissim is this. If a tornado's coming, you worry about how it's going to mess up your hair.
I tried to show the difference in intent: Seriousness versus frivolity.
Maybe it works for you. Or it might not. It works for me now.