A childhood belief about nationalities

When I was younger, I must have heard the expression "the British have stiff upper lips" somewhere, perhaps in an Altoids ad. However, not knowing that it was just a saying, I thought that British people, for some odd reason, actually HAD stiffer upper lips than most people, and if you touched them under the nose, their lips would feel hard, like muscle! I thought they must have very strong facial muscles to smile and frown with such hard lips!