I find that mastery is not always about winning but looking for improvement in every game. Sometimes it is experimentation and sometimes is it mentoring players no matter who they are.
I played a lot in the lead up to SCG Con and I lost some games because I showed my opponents how to beat me, I wanted them to play their best game and I needed to see how to counter it. I out played some high level people and still lost, but I still had fun. I also just won some games because in Vintage your deck will just crush people.
When playing at a level where everyone you play against is a master it is easy to see your flaws. That is where you truly need to notice your weaknesses - engagement, timing, sequencing, strategy, etc...
To me a true master, is someone who knows their deck and their own limitations. We all have limitations and it important to know them and so that you can expand your game and your range.
I mostly play Vintage but sometimes I play Legacy and Modern. I typically play at a high level but those formats do not keep me very engaged and I tend lose my motivation after a bit in large events.
I find that I am playing at my highest level when I am having fun. When I am playing only to win at any cost and I am not having fun then I am not a player that anyone wants to play against. It is important to have more purpose than just winning, I find that is not just good for playing Magic but generally good in life.