When I was at boarding school (why did you send me away at age ten, Dad?) we had to polish our shoes every day, and there was an inspection at assembly every morning. Now it wasn't like an army inspection, no-one seemed to expect a high polish, but Sunday was different as we all had to go to church and the inspection was more vigorous. Woe betide any boy who didn't have a well-shined pair of shoes. Because of this, the boys spent exra time Saturday evenings, buffing and spit-shining. The masters expected to see their faces in those shoes. This was the time when you could spot the army brats: they would start on Friday night, laying down many layers of shine before finishing up with a rag-finish, whipping a cotton cloth across the leather as though their lives depended on it, having been schooled by their fathers to get a parade mirror finish. As an RAF brat I'd also been taught The Way, of course. It seemed to me at the time to be a stupid way to have boys spend their time, but dull shoes at church parade would result in Consequences, at the very least being barred from leaving the school bounds and perhaps made to do extra chores, at worst a detention and extra homework. If we heard that the Latin master was running the morning show, every boy would spend extra time and elbow grease to get as deep a shine as possible because nobody wanted extra bloody Latin, even the swots.
Anyway, all this does have a purpose, because the masters knew the boys. They knew that on the winding path uphill to the church, the boys would be tempted to kick any stones they found in their way, and there'd be a master stationed at the church door to do a final check for properly-knotted ties and brightly shining toecaps. Any newly-obtained scuffs on that perfect shine and there would be ructions. Standards were high, and for the boys, stakes were high. No-one wanted to be caged for Sunday afternoon or evening, and yet that would be the punishment. Extra homework, extra duties (which could run from sweeping a corridor to scrubbing the showers) meant that our precious free time would be ripped from us.
All this is to say that each boy was unusually careful on the walk to church, even to the point of avoiding stones in the way. It was unnatural to not kick a stone, the temptation was so strong, our boy-instincts so finely tuned. Pandeism Fish is spot-on when they say it's instinctive. Somewhere in the deep past, I know that every dinosaur kicked stones for some un-knowable reason (shame they couldn't kick Really Big Rocks out of the way =\) and now it's in our genes.
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