One thing that has caught me off balance a few times is people from outside the U.S. generalizing from whatever one place they’ve visited or even lived in. I remember one man from somewhere in the Middle East going on at some length about how Americans are this and Americans do that. His depiction of Americans struck me as very odd, even though he had lived here for some years by then. I asked him what he was basing his impressions on, and he said, “Well, that’s what I’ve seen around here.” “Around here” was Silicon Valley. I had to explain to him that to the rest of the country, California is typically seen as a little strange and that most Americans would not fit his description at all. I don’t think he understood.
However, I imagine that even in the very smallest countries there are regional differences, starting with city folk versus country folk, and those effects are only going to be magnified in a multicultural society like ours. My guess is that people within any country are much more aware of their differences and people outside are much more aware of their similarities, exactly as it is all the way down to units as small as the family. I think my brothers look so different that you can’t tell they’re related; a friend looked at a picture of them together and said they look exactly alike.