Here's why:
* The pearl is the catalyst: The discovery of the pearl sets in motion a chain of events that ultimately lead to Coyotito's death. Kino's hopes for a better life are pinned on the pearl, but it also brings greed, envy, and violence.
* The attack: The attack on Kino's family by the trackers is a direct result of the pearl. It's the culmination of the danger and animosity the pearl has attracted.
* Coyotito's death: Coyotito is accidentally killed by a stray bullet during the attack. This is the ultimate tragedy, shattering Kino's dreams and pushing him to a breaking point.
* The turning point: Coyotito's death signifies a complete change in the story's direction. It leads to Kino's descent into rage and despair, ultimately ending with him throwing the pearl back into the ocean.
While there are other dramatic events in the novel, such as Kino's escape from the town and his encounter with the priest, Coyotito's death is the moment that changes everything. It represents the ultimate loss and the devastating price of the pearl.