This may have been covered in the thread about jazz improvisations, but I’m listening to Cream and thinking about all three members talk about how only the beginning and the end of their songs were set with almost everything in between being improvised. They also talk about there being basic chords and rudiments and building from there.
But, musicians, do you sometimes improvise and wonder at that moment or later when you hear a playback, “Where that that come from and how do I do it again?”. Ginger in particular always says he didn’t play the same thing twice.
In an interview a few years ago, when Clapton was asked about his playing on the Cream bootlegs, which are often far from the official recordings, he said that he was surprised at what he was capable of playing. When the interviewer asked if he wasn’t able to do that anymore, Clapton said it wasn’t that he couldn’t, he was just surprised as how he played.