A girl walked down the beach, where there were thousands of oysters left by the ocean. She took one and threw it in the water. A man walked by. He spopped and asked her, "What are you doing? There are too many of them. You'll never make a difference."

The girl picked another oyster up and threw it in the sea as far as she could. She turned around and smiled at the man. "I made a difference," she said, "for that one".

I heard this one in one of the commercials on TV, and liked it even though it was used to practically bribe the money out of people. The meaning is nice nonetheless. Anyway, I don't claim to have memorized it word for word, but it's pretty close.