Figured out at 34 that I'd been tying my shoes wrong my whole life
A guy at the climbing gym in Denver watched me lace up for 2 seconds and said "you know those loops are supposed to go the other way, right?" I thought he was messing with me. Turns out my bow was slipping loose all day because I was making a granny knot instead of a square knot. I sat there and retied my boots three times to prove him wrong and they held tight every single time. So what's the dumb little thing you found out you'd been doing backwards for years?