During the Eastern Han dynasty (25-- 220 A.D.) there was a poor pupil named Kung-sun Mu who was fond of studying. After he had reached certain stage, he wanted to go on to further study.
"But," he thought, "going to college requires a lot of money and my family's poor. Where can I come up with the money?
"I've got it! I heard there's a rich family that wants to hire workers to pound rice. I ought to go work there and save up some money, and then I'll still have time to go to college. Okay, I'll go to morrow. . . . dressed as a laborer!"
One day when the master came to inspect the workplace, he saw that Kung- sun Mu was gentle and refined in demeanor, not like a laborer at all. He asked and found out he was really a learned scholar.
Wu Yu was impressed with Kung-sun Mu's persistence and drive for learning. Talking happily in front of the mortar and pestle, they became friends.
At that time, when the concept of rich and poor classes was deeply ingrained, for Wu Yu to humble himself to make friends with a poor scholar can be considered quite extraordinary.
Later, people described a friendship between a rich person and a poor person as "a mortar-and-pestle friendship. "
