This is from Stephen Covey's Seven Habits of Highly Effective People and is a story I often think of when I fell I am being too judgmental of others.
One day, a ten-year-old boy went to an ice cream shop. The place was very busy and a waitress finally made her way to where he was seated. The boy thought for a time as the waitress impatiently waited for him to speak. Finally he asked the waitress, "How much is an ice-cream cone?"
She said, "seventy-five cents." The boy started counting the coins he had in his hand. The waitress became more and more annoyed as other customers waited. Then he asked how much a small cup of ice-cream was. The waitress impatiently replied, "sixty five cents."
The boy said, "I will have the small ice-cream cup." The waitress, irritated at how inconsiderate the boy was of her situation, brought him his ice cream and scurried to serve the other patrons. The little boy had his ice-cream, paid the bill and left. When the waitress came to pick up the empty plate, she was touched. Underneath were ten pennies as tip.