I give the Moonlight Sonata credit for me becoming a decent pianist. It was above my level when I was a kid, but I wanted to learn it, and my teacher encouraged that. With enough practice on a piece that was so far above my current ability, I
seriously leveled up as a pianist.
My teacher's ability to help me learn what I wanted to learn made me so invested in piano as a kid. Many kids don't stick with music because (IMO) they can't find a way to enjoy it or be invested in it. For me, what I enjoyed happened to be Beethoven, but at other times I just wanted to improvise various modern songs. (Which can be as simple or as complex as you want, but a lot of classically trained teachers can't/won't/don't teach improvisation.)
Technique and theory only get you so far. Being able to emotionally invest in your playing is what sets musicians apart, imo. And as you're growing as a musician (even when you're a kid), you're going to sound like shit if you just try to monotonously follow the instructions. I'm not sure enough music teachers get the importance of being personally and emotionally invested in the moment as you're playing. (One-buttock playing is a good word for this: https://youtu.be/r9LCwI5iErE)
The choice of what you want to play is pretty important in keeping you invested.