What event convinces Juana that they can never go back to the simplicity of life she and Kino experienced before he found the pearl? How does this event change things?

Kino strikes Juana in the face with his clenched fist and kicks her in the side. He then turns away from her and walks up the beach. Juana knows that when Kino said that he is a man, he meant that he was "half-insane and half-god" and knows as a woman that "the mountain would stand while the man broke himself; that the sea would surge while the man drowned in it." In this, the level-headed Juana realizes that Kino is a man raging against an obstacle as insurmountable as a mountain or a storm, and his struggles will only cause him to destroy himself.