Once upon a time there were two screws fastening a vital part of a gasoline engine. One of the screws was haughty and proud of it's shining head. The second screw was quiet, intent only on doing its job to the best of its ability.
One day a speck of rust appeared on the head of the second screw. Filled with vain pride of its own beauty, the first screw began to laugh at the second. "Your head is tarnished," the first said to the second. "Look at you. Your perfect luster is gone."
The second screw said nothing. Instead, it concentrated on what it was doing. "How ugly you have become," the first screw chortled, "and how beautiful I have remained." Then it began to laugh so hard at the second screw that it failed to notice that it was working itself loose. Finally it dropped off the engine and plunged into a small pool of dirty oil below.
With the first screw no longer holding up its end of the load, the second was faced with doing the work of two. Meanwhile the first screw, now covered with grimy oil, wailed and lamented. "Just look at me! I'm dirty and filthy and all my beauty is gone. By laughing at the blemish on my friend the second screw, I worked myself loose and fell into the muck. Now I'm doomed."
Now, it just so happened that a short time later the owner of the engine started it up. He immediately noticed that something didn't sound right -- the engine was running rough. When he checked, he instantly saw that one of the two screws holding the vital part was missing. "Ah ha!" the owner said. "One of the screws must have worked itself loose and fell to the ground, but I don't see it. Maybe it fell into that puddle of old oil."
The owner reached into the oil and found the missing screw. "Look at you," the owner said. "You're all covered with grime and oil. How ugly you are. But I will fix that right away." The owner reached for a nearby rag and wiped all the oil and grime off the first screw until it shone even brighter than before. Then he replaced it on the part. Before he turned away, he noticed a little speck of tarnish on the head of the second screw. With the second rag, he wiped the head clean and bright. Then the owner walked away.
Finally the engine was started. The two screws, now equally beautiful, held the part tight. "Forgive me, my friend," the first screw said to the second. "In my vanity, I was so busy laughing at your blemish that I did not notice that I was working myself loose."
"And what have you learned?" the second screw quietly asked.
"I learned not to judge others because I have my own sins to deal with."
"Then," the second screw said, "I forgive you."
"Thank you, my friend. And rest assured, my vanity will remain forever at the bottom of that dirty puddle of oil."