Billy commits suicide by slitting his throat with doctor's instruments after Nurse Ratched humiliates him and threatens to tell his mother about his encounter with a prostitute. Billy's intense fear of his mother's disapproval, exacerbated by his unhealthy, controlling relationship with her, drives him to take his own life to avoid the shame and guilt.

In One Flew Over the Cuckoo's Nest, the hospital used drug therapy, group therapy, electric shock therapy, and lobotomies. Drug therapy often left patients in stupors, and group therapy was dominated by Nurse Ratched, providing little benefit. Electric shock therapy and lobotomies, meant to calm patients, were extreme measures. Overall, these therapies were mostly ineffective, especially after McMurphy's death.

The importance of humor and laughter in Kesey's novel is to communicate the true feelings of the patients. They are all in a mental facility, but they still want to talk about their feelings, even if it seems like nothing to anyone else. The only way for them to do this is through humorous dialogue and actions.

After the fishing trip, Chief Bromden's experience with "the fog" changes significantly, as he gains mental clarity and a renewed sense of agency. Previously, he would linger in the fog for weeks after shock treatments, but post-trip, he quickly "fights" his way out, suggesting increased inner strength and purpose. This shift represents a newfound belief in his power to challenge the oppressive "Combine" and take control over his life, marking a crucial turning point in his character's journey.

The author is ambiguous about his sanity.

Ellis and Ruckly's conditions in One Flew Over the Cuckoo's Nest symbolize the dehumanizing effects of institutionalization. Ellis, who was once an Acute but is now a chronic, often stands nailed to the wall, representing crucifixion imagery. Ruckly, reduced to a vegetative state after a botched lobotomy, embodies the loss of individuality and humanity under oppressive control.

Chief Bromden pretends to be deaf and mute to avoid drawing attention to himself and to protect himself from the oppressive control of the mental institution. Over time, this act becomes a part of his identity, symbolizing his loss of individuality and resistance to authority. His journey reflects his internal struggle and the dehumanizing effects of the institution.

Chief Bromden's schizophrenia in One Flew Over the Cuckoo's Nest is depicted through his hallucinations and paranoia, which symbolize his perception of societal control and dehumanization. His condition reflects the oppressive environment of the mental institution and his struggle to reclaim his identity and autonomy.

One Flew Over the Cuckoo's Nest explores themes of mental disorders and societal pressures, suggesting that what is deemed "insanity" often results from societal stress rather than inherent mental illness. The protagonist, McMurphy, challenges the oppressive norms of the psychiatric hospital, symbolizing society's attempts to enforce conformity. The novel critiques psychiatric practices and influenced changes in mental health care, promoting patient autonomy and reducing institutionalization in favor of community-based approaches.

The themes in One Flew Over the Cuckoo's Nest challenge the reader's perception of reality by exploring the fine line between sanity and insanity. The novel questions societal norms and the power structures within mental institutions, suggesting that what is deemed "normal" can be subjective and manipulated by those in authority.