I’m cheating here a bit, because it wasn’t in school. Instead, I fondly remember my bass guitar instructor who, after 10 lessons said:
“Structured learning isn’t for everyone, I think you’d get bored of me teaching you scales very quickly. Join a band, jam, screw up. Most musicians learn so much more from that experience than anything I can offer.”
It opened my eyes to the notion that different people learn very differently on different topics. I need the structure of a course to succeed in topics like analytics or languages, but in music or leadership osmosis and experience trump any book I could read.