Depending on your interpretation, and your mood, a smile may not be such a small thing. It takes about 20 muscles to smile so it's not a trifle. However, the mental power required to generate one, to get those muscles doing their thing, can sometimes be enormous, particularly if you haven't had much practice or if you are feeling decidedly un-smiley.
I think a smile is a mighty weapon which can be used for both good and evil purposes, but because I do not want to make you frown, I wish to focus on the positive aspects of the upside frown.
1. Smiling is easy. Forget everything else I said, and remember this: it really isn't very difficult to muster a smile, even when you don't really feel like.
2. Smiles are free. Although costing nothing, they can achieve a great deal.
3. Smiling makes you feel better. I read somewhere (so it must be true), that forcing a smile when you need to can actually generate some positive energy and make you want to smile.
4. Smiles are contagious.
What makes you smile? What made you smile today?