The Buddha said that craving is like holding a torch against the wind; the fire will burn you. When someone is thirsty and drinks only salty water, the more he drinks, the thirstier he becomes. If we run after money, for example, we think that a certain amount of money will make us happy. But once we have that amount, it's not enough; we think we need more. There are people who have a lot of money, but they are not happy at all. The Buddha said that the object of our craving is like a bone without flesh. A dog can chew and chew on that bone and never feel satisfied.