AFAIK it all boils down to the fact that during embryonal development our cells, which at that point were just a blob of undifferentiated autonomous chemical machines, somehow managed to unanimously agree upon the cardinal directions (up-down, left-right, front-back) for future development - and thanks to this, we don’t have toes growing out of our ears.
That’s why there is an entire community for shower thoughts: because people sometimes get these sudden realizations. But honestly, you got me - I realized it a few days ago and only got around to post it “now”.