Years ago I was in a session when I suddenly turned around to my clients and asked, "What is it that you think you are paying me for right now?" They came up with a few answers relating to time, recording gear, the space we were in, and such. I laughed and said, "Sure, sort of. But I think what you are really paying me for is every mistake that I've ever made on a session before, and am (hopefully) not making right now on yours." We had a good chuckle and kept plugging away on the overdubs at hand.