A man made his living painting barns, but he decided he wasn't making enough money. He realized he couldn't work any faster, so he decided to add water to the paint to make it go further and thereby increase his profits.
All went well for a while, until one day he woke up after a big rainstorm. He went out to look at the last barn he had painted, and sure enough, his work hadn't held up. The paint had come off and the walls were all streaky.
All of a sudden, a lightning bolt struck the ground near where the man was standing. As he jumped back in terror, a voice spoke:
"Repaint, and thin no more!"