Tu Gu Hun in ancient times was located in what is now the Songpan area of Qinghai and Sichuan Provinces.
A'cai, the chief of Tu Gu Hun, had twenty sons. One day, he said to them, "Each of you, bring me an arrow."
He then broke the arrows one by one and threw them on the ground.
After a while, A'cai said to his half-brother Mu Liyan, "Take one arrow and break it."
Mu Liyan broke it effortlessly. "Now bring nineteen arrows and try to break them all at once," A'cai demanded.
This time, despite all his efforts, Mu Liyan could not break the bundle.
Thereupon, A'cai said meaningfully, "Do you understand why? A single arrow is easily broken, but bound together, they become unbreakable. As long as you cooperate fully and remain united in purpose, our kingdom will endure for generations."