I would say it is the terrible weather, too cold in winter, too hot in summer. It probably means something like "serious people are the rulers, because if you do stupid crazy things you are dead" over thousands of years that forge a culture.

Russia is so big, and yet so ugly. I took the transsiberian train and it was so boring. In 40kms of Chile you see more than in 3000 of transsiberian. In Winter there is no light, and no color(snow everywhere).

When you travel to places where the sun shines all year long you find that everybody smiles so much. You go to Bali, Brazil, Cuba, Costa Rica, kenia, Nigeria, all people smile all the time.

Boston, New York,Seattle, Germany, they are in the middle-upper scale of seriousness. Miami, California, less serious.