It’s as if you noticed that happy people tend to smile more than unhappy people, so you invented a device that stretched the human face into a smile as a cure for depression. Yes, the smile is a good marker for happiness. Yes, there’s a correlation between smiling and happiness. Yes, it’s possible that reminding yourself to smile more can affect your mood. But isolating the smile and ignoring all other factors that might contribute to happiness and depression is patently ridiculous.
