Some number of years ago, I heard a woman on NPR (best thing to listen to whilst working out) talking about how some study had concluded that when people smile, there is an increased production (or release) of endorphines (or something similar). so in effect when people smile, there is an actual physiological response, an increased sense of wellbeing. In other words, smiling makes you happy. I was interested in what other people might think of this. I find it to be true.