My writing only started improving after getting out of English class and replacing cultured reading with mediocre fanfiction.

Same thing in music - I'd do stuff in my own terrible demos, then hear other people's terrible demos and go "... ah, that's why good music doesn't do that." It's like there's a whole heap of bad ideas that people try out, and mediocre works are where you'll find the mistakes of others to learn from.

(It used to be a lot harder to find terrible demos before the Internet. The slush pile at the local community radio station helped, for example. Even the bottom 10% of a review pile - my previous sample of the bottom of the barrel - was at least in the barrel.)