For me the big eye-opener was learning to play traditional Irish dance music on whistle. About two years into the process, I thought I was great. I could read

For me the big eye-opener was learning to play traditional Irish dance music on whistle. About two years into the process, I thought I was great. I could read sheet music, I could play fast, I could play rolls, I knew a couple hundred tunes! Clearly I had to just keep it up at the same rate a few more years and I'd be a master. And then, about two years after that, it gradually sunk in that I'd been missing everything about what the music was really about. I hadn't been able to pick out what made good playing good, so I couldn't tell that my playing wasn't. I had been focusing on a bunch of superficial stuff and missing the heart of the thing. And now 20+ years on, I am vastly better at it than I was when I thought I was great. But I know there are loads of people much better. And I'm constantly worried there's some other epiphany waiting to happen when I will realize I'm still missing something absolutely key...