Why must Moon Shadow and his father leave the company?

For the first several years of his life in America, Moon Shadow lives with his father in the laundry that is owned by his father's uncle and several friends and relatives. Moon Shadow goes along with his father to make deliveries and pick up dirty laundry. When Moon Shadow is older, he is given the task of collecting past monies due to the company. During one of these outings, Moon Shadow is beaten and robbed by his cousin who has an opium addiction. Windrider goes after the cousin, threatening to kill him, but is stopped by the gang to which his cousin belongs. This causes Windrider and Moon Shadow to move away from the company or face retribution from the gang.