Common courtesy: How 'common' is it?

A simple “thank you” for a simple act the other day bothered me.

Early one recent Friday morning, on a warm spring day, I decided, during a round of errands in my New York City neighborhood, to buy a few items for Shabbat at a small kosher grocery store a few blocks from my apartment building. As I entered the glass door at front of the store, I could see a small crowd of shoppers already in line, getting their necessities for their Shabbos meals.

Someone coming in my direction also caught my eye — a young frum woman, tichel upon her head, pushing a baby carriage while holding a few plastic ba...