The story tells of a farmer long ago who worked in the fields. After working for a while, he soon became tired and went to rest against a tree. It was not long before a careless hare rammed into the tree, and died.
Upon seeing this, the farmer became very happy and took the hare home for his next meal. He realized that he didn't have to lift a finger to get a good meal, and he didn't have to work so hard to eat well.
Ever since that day, the farmer never worked again. He spent every day waiting underneath the tree for a careless hare, but never saw another hare. Even so, he continued to not work and wait under the tree for the rest of his life.
This idiom suggests that one should not depend on luck to become successful, and that hard work is required. Those who depend on chance and are lazy will not get what they need.