An Unfinished Self Portrait

I often advise younger artists to use themselves as models if other models are hard to come by, and when I was younger I found my own physiognomy the most fascinating subject to draw and paint. But now, as I am getting older I find it much more difficult to raise the enthusiasm to do self portraits.
I wonder is it to do with simple vanity or the lack of it as I mature? Now I rarely look in the mirror if I'm not brushing my teeth.
Or is it something to do with the difficulty of confronting what we have become rather than looking at the potential that we all have as youngsters.
Anyway, here's an unfinished self portrait that I managed recently.