[ohyes]

"I hit a plateau..." "I haven't picked up my dulcimer in several months"

In my experience learning instruments follows a 90/10 sort of rule, you can get the easy stuff in a matter of weeks, the harder stuff is subject to severe diminishing returns. You have to practice much more to make the relevant progress. That virtuoso is not a virtuoso because he practiced as a child when he had neuro plasticity, he's a virtuoso because he practices hours a day and then thinks about his practicing when he's not practicing. Even someone who is a moderately good professional does this.

[jakobegger]

Same for sports. You'll improve extremely quickly in the beginning, then you'll hit a plateau and you have to train much longer and harder to improve.