When one person smiles at another, the other person will generally smile in return. There is no hard and fast rule that this must be true. It is just a reaction many people have when they are smiled at. It may seem odd to go around smiling at strangers, and yet it is an act of creating beauty and happiness. Those smiled at may feel happy that someone smiled at them, and the pleasure they get is returned when they smile back. It is a wonderful way to change the world into a happier place.
Growing or maintaining a neutral expression has become fairly normal in most modern societies. Smiling at strangers is not something many people do these days, and yet it can have a positive effect. When people smile, their happiness often increases. It can make them more beautiful as their own inner light shines through. Walking through the world and smiling at just a few people could help uplift an entire city if enough people choose to give it a try.