http://www.amazon.com/Effortless-Mastery-Kenny-Werner/dp/156...
Got to play with Kenny at a jam thing a decade ago. Absolutely amazing experience.
There is so much that I can extrapolate on this subject, but I believe the greatest hurdle for a serious musician is that after you master all the dexterity, independence and music theory, the biggest hurdle is your own fucking self.
Even the greatest Jazz legends would typically say they only had a handful of performances in their career where they were really satisfied and where everything came together and worked perfectly. And these were musicians who practiced hours on end each and every day, on top of performing. Truly humbling.