Cultural Malaise

While walking home today, I was practicing smiling (smile, release; smile, release). It was the end of the day and I was a bit tired, so my face was flat. This reminded me of when I was in grade school and the schools were trying to teach us to smile. I remember they tried to play on our laziness by telling us that it takes fewer muscles to smile than to frown. They also told us to turn our frowns upside down. Why did they have to tell us to smile? What was wrong with us?