During the time of the south-north Dynasty, there was a kingdom called Tuguhun, which had been founded by the Xianbei ethnic group in the north western frontier region. Acai was the ruler of this kingdom.
Acai had twenty sons, every one of them was strong and possessed combative abilities. Each one of them had his unique skills. When Acai was very ill, he called all his sons to a gathering and asked each one of them to give him an arrow. He then asked his younger brother, Mu Liyan: “Please take one of these arrows here and break it.” Mu Liyan broke the arrow with ease. Acai then said: “Please take the nineteen arrows and break them apart.” Mu Liyan was not able to break that bunch of arrows. Acai explained: “Do you understand now? One arrow can very easily be broken, while a bunch of arrows is difficult to break. As long as all of them work together with one heart, our kingdom will be stable.”
According to Acai “one arrow can very easily be broken, while a bunch of arrows is difficult to break” and people of ancient times have said that “when the hearts of people are united, then even mount Tai can be moved,” this signifies the importance that people should work together as one heart.