This is my favorite Cat Stevens song, and I've always wanted to know his own thoughts on it. I looked up an older interview and he said Lisa is actually himself--inside himself.

At the time, I believe he was going through a depression, drinking too much and struggling with how the "business" was whoring his music.

I always thought maybe Lisa was a ghost or his muse. "Though I know no one can see her", makes perfect sense when you see it as an imagined female version of his own saddness inside. We all struggle with our own "ghosts". I still adore the song and Sir Stevens.