Great replies above. My perspective is, it depends on how well you know the material. I do gigs every week with a whole range of artists who bring varying levels of expectation to each gig. If I get called to solo on a blues, I am in the zone and am playing entirely my own ideas executed by ear etc. If I am playing rhtyhm changes at 320 bpm, like I was last week with Simon Spillett, I am using a much higher degree of muscle memory interspersed with bullshit. If I am on a ballad I don't know with a range of complex harmonies, I am invariably crashing and burning It's all of the above. Some of my solos are strong, some are weak and some are total trainwrecks. Improvisation is, by definition, a high risk undertaking and you are going to be unhappy with what you do most of the time. It's the thrill of the chase as much as it is the winning. I cannot, for instance, do anything meaningful with Giant Steps. Too fast, too complex for my little ears. I know some very competent players who can get through it but who feel the same; it's maths not music. Then you hear someone like Chris Potter do it and you think 'I am a w*****'.