Whenever I get discouraged by the many, many, many problems in the world, I think of this story:
A little boy was on the beach after a terrible storm. Thousands of starfish had been washed up on the sandy beach. The little boy started picking starfish up one by one and throwing them back into the water.
A man watching the little boy's efforts thought, "There are so many starfish and only one little boy. He will never help them all." The man walked over to the boy and said, "Don't you know you will never make a difference? There are too many starfish washed up on the beach."
The little boy looked at the old man for a long moment. Then he picked up another starfish, threw it into the water, and said, "I made a difference to that one."