Final answer:
The doctor in 'Don Quixote' believes that excessive reading of books of chivalry and resulting delusions are "killing" Don Quixote, leading to his mental deterioration and eventual demise.
Step-by-step explanation:
The student is asking about the perceived cause of Don Quixote's demise from the perspective of a doctor within the novel. In Don Quixote, it is suggested that the doctor believes Don Quixote is being "killed" by his disordered reading, particularly of books of chivalry, which lead him to his delusions and misadventures. He thinks that these stories have affected Quixote's rationale causing him to lose touch with reality.
This reading strains his mental health, leading to his eventual death. Don Quixote's fixation with the chivalric tales he has read culminates in a series of quests that he undertakes, believing he is a knight performing noble deeds, which ultimately contributes to his decline.