[CydeWeys]

An interstate takes a lot of time and effort to build. And yet which side you drive on doesn't matter; it simply needs to be consistent with all the other roads you're connected to. There are plenty of countries that, through historical happenstance, drive on the opposite side of the road, and it's fine.

So in other words, just because the staircases take a lot of time and effort to build, simply means that having the staircase itself is important, not necessarily that its chirality is important. It has to have a chirality but it may well not matter which one, just like roads.

[ramblenode]

Your example misses the point.

If there were evidence that driving on the right side or left side of the road slightly reduces car accidents and a country with previously no roads or cars began planning to automotize the country, then, all things considered, it would make sense to have people drive in the lane with a slightly reduced fatality rate.

If there are two choices where one presents a slight advantage but no additional cost then a rational actor will go with that choice.

[qwytw]

The event has to occur relatively frequently for that slight advantage to become statistically noticeable. Direct assaults on castles with hand-to-hand combat occurring in stairwells were extremely rare as far as we know.