The story of a butterfly named "Maculinea Arion" is most instructive. The creature lays its eggs on a plant, and after feeding on the plant for several weeks the young caterpillar makes its way to the ground. In order to complete its development, it must meet a certain kind of ant. When such an ant meets the caterpillar, the ant strokes it with its antennae, and the caterpillar exudes a sweet fluid from a special gland on its tenth segment. Apparently the ant likes this substance, because it then carries the caterpillar home to its nest. There the ants drink the sweet fluid exuded by the caterpillar. And, what does the caterpillar eat? The baby ants. The ants show their appreciation to the caterpillar by letting him spend the winter in a special cavity of their nest. It continues to eat the young ants until spring. Eventually it emerges as an adult butterfly and flies away to establish more of its kind. And the cycle starts all over again

Some people are not much different form the ants. For you see, they cherish a luxury item to the injury of themselves.