Until adulthood I thought I was literally physically incapable of running more than about ten feet because PE does not teach you how to run; it just assumes you already can! …and it turns out I really enjoy running

My sister said something similar, though she was describing it in time rather than distance

Ditto! I spent years thinking I was "bad at physical activities", it turned out I was just "bad at the things they do in PE". Though I do remember shocking the PE teacher when we did some kind of circuit training/fitness test and it revealed that I was actually quite fit. SURELY SOME MISTAKE.

I feel seen. (Not unfit, but moderately inactive due to desk job, and it took me until middle age to discover that running could be something other than torture, punishment or a last resort due to waterlogged pitches)