Two shopkeepers were bitter rivals. Their stores were directly across the street from each other, and they would spend each day keeping track of each other's business. If one got a customer, he would smile in triumph at his rival.
One night an angel appeared to one of the shopkeepers in a dream and said, "I will give you anything you ask, but whatever you receive, your competitor will receive twice as much. Would you be rich? You can be very rich, but he will be twice as wealthy. Do you wish to live a long and healthy life? You can, but his life will be longer and healthier. What is your desire?"
The man frowned, thought for a moment, and then said, "Here is my request: Strike me blind in one eye!"
One sign of jealousy is when it's easier to show sympathy and "weep with those who weep" than it is to exhibit joy and "rejoice with those who rejoice."