Oh, that... however, it does have a great deal to do with mind/ body problems, and in particular where the material for a great interpretation comes from. For example, a great player can bollox things up, grab hold of that, rescue it from the flames and get back on track, and the punters (even the cognoscenti, the equals who make up the session) only hear a great new take on the tune.

Other times, you'll do that process in your head, in bed or on the bog, so only the polished result gets heard in public. And then as often as not you'll wonder why it didn't go as well as expected.

The thing to take issue with is "simply". Nothing simple about sessions.