I can think of nothing Kino gained from finding the pearl, except for some momentary impossible dreams. He did, however, lose almost everything of value to him. By the conclusion of the novel, Kino has lost his home, his canoe, his life in his village, and his freedom to live in peace. He has killed men and beaten his wife. His baby is dead. All that is left of Kino's old life is Juana. Holding her dead son in his bloody shawl, she walks with Kino back to their village and to the water's edge to throw the pearl back into the sea.
Kino realizes, too late, that his happiness had not lain in the pearl and the wealth it promised. His happiness had lain in the Song of the Family that had filled him with peace:
Sometimes it rose to an aching chord that caught the throat, saying this is safety, this is warmth, this is the Whole.
Kino had said that the beautiful great pearl had become his very soul. When he returns it to the ocean, he sees it as a thing of evil:
He looked into its surface and it was gray and ulcerous. Evil faces peered from it into his eyes, and he saw the light of burning. And in the surface of the pearl he saw the frantic eyes of the man in the pool. And in the surface of the pearl he saw Coyotito lying in the little cave with the top of his head shot away. And the pearl was ugly; it was gray, like a malignant growth. And Kino heard the music of the pearl, distorted and insane.
By throwing the pearl back into the sea, Kino seeks to save his soul and find his way back to the man he once had been. This is an act of wisdom, the wisdom Kino had gained through profound suffering and loss.