I still don't understand why Americans don't take their dirty shoes off when they walk around their nicely carpeted houses
Having visited Saint Petersburg recently, I noticed this: THERE IS DIRT EVERYWHERE! For example, outside Площадь Восстания, there is a small very busy, very dirty street. However, I didn't see any genuine soil around. The main problem is that all this dirt is just dust from the vehicles. In America, we wear our shoes to the car, following a clean sidewalk. Then we drive to our destination. We then walk to the house, following another clean path. Our shoes are not yet dirty! However, if it is raining or our shoes get dirty we remove them.
My house has very clean floors and we wear our shoes often. Also, in my dormitory, the floor is so heavily carpeted by stray papers that no dirt actually makes it to the floor.