Entrepreneurship is mastering - if anything - "operating" in extremely uncertain and risky conditions. There's no tangible hard skill you're mastering. It's fulfilling - but personally completely void of the feeling I've had truly "mastering" a sport. (I'll use "mastery" loosely here - I wasn't nearly good enough to play pro. It's a completely different feeling than "mastering" a subject such as physics or calculus (again using "mastery" loosely). Perhaps mastery of soft skills leaves me a bit void and its the hard skills that entrepreneurship lacks.