The first person narration is one clue to the answer to this question. Even though McMurphy manages to shake things up at the hospital, allowing some of the patients to stand up for themselves and enjoy life, it also causes tragedy when one young man commits suicide. In the end, McMurphy's personality is changed and his voice subdued; Bromden preserves the memory of McMurphy by making sure he does go on in this incapacitated state. This confers a heroic status upon him for sacrificing his own love for McMurphy to make sure his friend does not live on in a pathetic way. Also, when Bromdem smashes the wall and escapes, leaving the possibility of escape for others, he becomes a hero in the physical sense.