Legend has it that the Ketagalan forebears originally lived on another island. One day, a monster appeared on the island. Every night it would appear in the village, terrorizing the villagers. Accordingly, the villagers laid traps for the monster all around their homes and fields. The wounded monster was forced back into the mountains and the village was peaceful again for a while, but soon afterward it reappeared. Pushed to insanity by hunger, the monster went into one of the village homes and killed a child. The villagers lived in fear of being eaten and did not dare to sleep. The villagers fiercely debated but nobody could think of a way to deal with the monster.
With no other choice, it was decided that they must pack up and leave the island. Following an arduous sea voyage, they sighted land. The island they landed on was Taiwan. Many years later, the tribe was growing so one day the villagers agreed to draw straws. Those who drew long straws were permitted to remain living on the fertile plain while those drawing the short straws would have to move into the mountains. Thereafter, the villagers were separated into plain-dwelling and mountain-dwelling tribes.