Long long ago, an old man kept a group of monkeys. He understood them very well and had great fun with them. Everyday the old man treated the monkeys by feeding them acorns. They were all very, very happy.
Soon the old man's supply of acorns began to run out. He decided to cut their rations. One day, the old man asked his monkeys: "From now on, I will give each of you three acorns in the morning and four in the evening. What do you say to that?" Blinking their eyes, the monkeys looked at one another and clattered angrily. "I'm sorry." The old man said with a smile. "Calm down. Calm down. How about four for breakfast and three for supper?"
The monkeys quieted down and looked much more content. They jumped happily around their master as if they have been promised more nice food.
From this fable comes the idiom Zhao San Mu Si. At first the phrase was used to illustrate the idea that the wise are good at tricks, and the foolish are easily taken in. But now, the idiom is used for someone who doesn't know his own mind and changes all the time.