The title comes from a child’s rhyme, which also serves as the epigraph. The epigraph reads "One flew east, one flew west, / One flew over the cuckoo’s nest." Since the title is only the second half of the epigraph, "one flew over the cuckoo’s nest" must be the portion of the rhyme that Kesey felt was most important. Flying over the cuckoo’s nest is probably a way of expressing that someone is crazy (think back to elementary school when you’d call people "cuckoo" as an insult). The character who goes crazy in the end of the book isn’t the narrator, Chief—by the closing of the novel he’s remarkably sane. McMurphy, the guy who enters the ward seeming pretty sane, although mischievous, ends up being lobotomized. As a result, McMurphy is probably the character who "flew over the cuckoo’s nest."