Mastery is a strange term. For example, most people would recognize that to be a professional athlete you must have mastered that sport. Yet, at the same time,

Mastery is a strange term. For example, most people would recognize that to be a professional athlete you must have mastered that sport. Yet, at the same time, within that professional level there are often a select few all-stars or champions that stand out amongst the field. So, Steve Jobs in charge during the Mac era vs Steve Jobs as CEO of Pixar vs Steve Jobs CEO of Next vs. Steve Jobs as CEO of Apple during the iMac/iPod/iPhone era is certainly different levels of mastery. At what point did Steve Jobs "master" the art of running a company? You can certainly look back a decade or more and see him doing much the same things then as he is now. Yet, he clearly is a more successful CEO now than 10 or 20 years ago. Perhaps mastery would be better defined as attaining a level of capability in all the required skills required of a particular job/skillset. Mastery is often the point of diminishing returns where you spend minimal time learning new skills and most of your time refining your skills and methods further.