“The legend of the three arrows” is a, most likely apocryphal, story about the sengoku daimyo of the Chugoku region Mōri Motonari.
In hope of encouraging three of his sons, Mōri Takamoto, Kikkawa Motoharu, and Kobayakawa Takakage, to work together for the benefit of the Mōri clan. Mōri is said to have handed each of his sons an arrow and asked each snap it. After each snapped his arrow, Motonari produced three arrows and asked his sons to snap all three at once. When they were unable to do so, Motonari explained that one arrow could be broken easily, but three arrows held together could not.
It is a lesson that is still taught today in Japanese schools and is believed to have been a source of inspiration for Akira Kurosawa when writing his epic film Ran.