While McMurphy laughs. Rocking farther and farther backward against the cabin top, spreading his laugh out across the water—laughing at the girl, the guys, at George, at me sucking my bleeding thumb, at the captain back at the pier and the bicycle rider and the service-station guys and the five thousand houses and the Big Nurse and all of it. Because he knows you have to laugh at the things that hurt you just to keep yourself in balance, just to keep the world from running you plumb crazy.

While on the fishing expedition, the patients are able to laugh freely and feel like whole humans again. As usual, this happens with McMurphy’s guidance—he is an example for all the patients to follow. Here, Bromden shows how McMurphy’s booming laughter in the face of chaos, which could be seen as the mark of a psychopath, is the one thing that keeps McMurphy sane.

Bromden implies that it is the pressures of society—the captain, the five thousand houses, the Big Nurse, “the things that hurt you”—that drive people insane. To maintain sanity in such an oppressive and cruel world, people cannot allow these external forces to exert too much power. When a person succumbs to seeing and experiencing all the sadness and suffering of humanity, as Bromden has done for ten years, it naturally makes him or her unable, or unwilling, to cope with reality—in other words, it can make that person “plumb crazy.”