Smiles are contagious. They can help you maintain a sunny disposition and also have the effect of making people respond to you in a positive rather than negative way.
We may forget to smile when we are in a hurry or at the end of the day when we are tired. It is hard to smile when we are sad, but when dealing with strangers and other people, a smile may help brighten the day and provide us a friendlier environment in which to communicate or work in.
Here is a Lego smiley man to help you remember to smile more.