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.

~Author Unknown