In the book Half the Sky, they end one of the chapters with this well known story:
A man goes out on the beach and see that it is covered with starfish that have washed up in the tide. A little boy is walking along, picking them up and throwing them back into the water.
“What are you doing, son?” the man asks. “You see how many starfish there are? You’ll never make a difference.”
The boy paused thoughtfully, and picked up another starfish and threw it into the ocean.
“It sure made a difference to that one,” he said.