An accident could happen to these oysters, a grain of sand could lie in the folds of muscle and irritate the flesh until in self-protection the flesh coated the grain with a layer of smooth cement. But once started, the flesh continued to coat the foreign body until it fell free in some tidal flurry or until the oyster was destroyed. For centuries men had dived down and torn the oysters from the beds and ripped them open, looking for the coated grains of sand. Swarms of fish lived near the bed to live near the oysters thrown back by the searching men and to nibble at the shining inner shells. But the pearls were accidents, and the finding of one was luck, a little pat on the back by God or the gods or both.
― John Steinbeck, The Pearl