I doubt that it is possible to fully master an art form.
Decades after I was first acclaimed as an award-winning author I am aware of how much I still need to learn. today I'll watch more photoshop tutorials to improve my ebook cover design abilities.
The Japanese say that the apprenticeship to become a master in the creative arts is 40 years, and you start at age ten and are not considered a master until you are 50. I have been an artist all my life and in my 70th year, I still have more to learn that I know. Mind you; I have been 'professional,' for many years—but it takes a lot more that 10,000 hours to have all the skills we need for our creative professions.
Mantra: Keep learning, continue to practice and improve. The day you think you know it all is the day you start to decline.
I once added sculpture and pottery to my creative skills and in doing so I studied the Japanese discipline, as I considered them the masters of the art form. With that forty year apprenticeship, it's no wonder they remain the masters of the art.
I once asked a painting instructor how to do something. He picked up a tool and accomplished the technique in a second.
I gasped in excitement. "That is how—"
"No,'" he snapped, "forty years of doing that is how you achieve the effect."
I had good teachers and I've practiced hard.