The absolute cruellest thing about learning a musical instrument as an adult (who didn’t study much music at school) is the inescapable fact that you have to practice being really, really, really shit at it for an *awfully* long time before you can reach a level of competence that even approaches adequacy.
@herdingdata
The difference there is that children learning to play an instrument are just as bad for just as long but just don't care because they are used to it & in as much as they do care value improvement over some absolute standard.
It also helps that they can often spend more time on it, so more quickly getting through the X hundred hours to achieve competency.