A random act of kindness is a selfless deed performed out of concern for the welfare of others. It is performed voluntarily and usually on the spur of the moment. We perform these acts without expecting any form of physical reward and more often than not we do it to strangers.
The other day I was walking through town when I came across a man lying on the pavement with a small crowd milling around him. The guy was drunk and had lost balance, hitting his head on the pavement as he fell. His head was bleeding and he wasn't moving. I paid a taxi to take him to hospital, checked him in with my details and then went home. On the day of his release I got a call from his wife and I met the whole family in hospital. The emotional outpouring of gratitude really touched me and it was then that I realized the magnitude of my magnanimous deed. At that moment no other form of reward would have replaced the wonderful feeling inside me. We are naturally programmed to help others once in a while.
Random acts of kindness are good because neither the helper nor the person being helped has to worry about obligation or resentment. These acts of kindness benefit both the giver and receiver. As the helper one benefits from enhanced self-esteem when we see our kindness helping someone else.