Why is the finding of a pearl an "accident?"

Kino's occupation as a pearl diver demonstrates the small chance that he and his family have for success. Pearl diving is a largely fruitless task that relies on the small chance for finding suitable oysters undersea and generally offers only the bare sustenance that maintains Juana and Kino. In effect, pearl diving is an act of desperation that further bolsters descriptions of Kino's poverty. It is the only hope that Kino and Juana have.