I was teaching a few piano classes at a local community college and the head of the music department got a phone call one morning. A beauty pageant winner was supposed to sing some songs at a business luncheon, but her regular piano accompanist woke up ill and couldn't perform. The caller was her manager, and he was desperate to locate anyone who could play the piano behind her.
I agreed to try it, but I couldn't guarantee how well it would go. A piano accompanist usually works with a solo singer for so long that they can practically read each other's minds. I met this woman at 10am and the luncheon was scheduled for 12:30pm. Her manager had the accompanist sheet music available, so I spent a few minutes sight-reading it. We rehearsed her performance for about an hour, then I met her again at the hotel. The show was a little shaky in places, but we did get through it. I don't know if I could do that for a living, though.