What you put out in the world is what you get back. Why not give yourself some happiness by smiling? Smile at a friendly-looking stranger and see what you get back – I bet it will be a return smile.
Smiling is easier than frowning – it takes many fewer muscles to smile than it does to frown. And it makes you feel better psychologically. Think you can feel depressed when your head is up and you’re smiling? Just try it. I bet you can’t.