It's extremely rare for a film to win all five major Academy Awards: Best Picture, Actor, Actress, Director and Screenplay. 'One Flew Over the Cuckoo's Nest' in 1975 became only the second film to do so, and the feat didn't get repeated until 1991 when 'The Silence of the Lambs' won all five. Some would argue that it is even more impressive that the film is as good as the Ken Kesey book it was based upon, while also honoring the story but maintaining its own unique voice.
Kesey wrote the book after working the graveyard shift as an orderly at a mental health facility in Menlo Park, California. He became sympathetic to those interned there, and that inspired him to write a novel from a patient's viewpoint. Although he worked in California, Kesey hailed from Oregon and set the story in his home state. The book is written from the point-of-view of Chief Bromden, a silent Native American inmate, but the protagonist is Patrick McMurphy (Jack Nicholson).