A smile costs nothing but gives much. It enriches those who receive without making poorer those who give. It takes but a moment, but the memory of it sometimes lasts forever. None is so rich or mighty that he cannot get along without it and none is so poor that he cannot be made rich by it. Yet a smile cannot be bought, begged, borrowed, or stolen, for it is something that is of no value to anyone until it is given away. Some people are too tired to give you a smile. Give them one of yours, as none needs a smile so much as he who has no more to give.

Got this from "Life is Wonderful" blog