how does insanity relate to the book?

I think that the whole concept of insanity is blurred in a place like the mental hospital. Patience like McMurphy and Chief Bromden go in sane yet develop the conditions they are labeled with while inside. The term "crazy" is hence used as a sort of capital to be bartered or used for leverage between Nurse Ratchet and the other patients. Check out my other answer that expands on this in the link below,

http://www.gradesaver.com/one-flew-over-the-cuckoos-nest/q-and-a/are-there-any-conflicting-viewpoints-expressed-in-the-book-with-theme-of-madness-if-so-what-are-they-100595/