One essential question of John Steinbeck's Of Mice and Men, published in 1937 is under what circumstances mercy killing is justified. This question is demonstrated by the protagonists George Milton and Lennie Small, an unlikely friendship that is forged out of their mutual ill-fated circumstances as migrant workers amid the Great Depression and dust bowl landscape. They are going to work on a farm in Salinas, California (the home of John Steinbeck), as many migrant workers fled to California in search of work, encountering meager wages and larger, mechanized farms.
Lennie is the physically larger of the two, and is mentally retarded, which compromises his situation even more than his financial limitations do. For this reason, George Milton takes care of him, as he promised Lennie's Aunt Clara that he would do so. George nobly assumes this charge, giving Lennie (and himself) hope by speaking of a ranch that they will both have one day.
Lennie accidentally kills a puppy owing to his brute force, and, despite his retardation, he realizes his mistake, and says,
"Why do you got to get killed? You ain't so little as mice. I didn't bounce you hard." He bent the pup's head up and looked in its face, and he said to it, "Now maybe George ain't gonna let me tend no rabbits, if he fin's out you got killed." (Chapter 5).
Lennie then tries to cover the puppy in a mound of hay, knowing the error of his ways. This death foreshadows his accidental killing of a human, Curley's wife (who has no name, which positions her narratively for an obvious death).
In the novel's final, poignant scene, Lennie sees a vision of his aunt, chastising him for doing "bad things" (Chapter 6). When George appears to join at him at the camp, Lennie pitifully implores, "You ain't gonna leave me, are ya, George? I know you ain't." Meanwhile, a giant rabbit--an absurdist representation of Lennie's own conscious--says that George will indeed leave him, and calls Lennie a "crazy bastard." The imaginary rabbit's calling Lennie crazy in some ways formally sanctions George's killing. George has demonstrated for the novel's duration his unabated commitment to Lennie's care, even if the face of consistent misfortunes caused by the unwitting Lennie. Only when Lennie faces the justice of Curley and the authorities for the death of Curley's wife does George take the initiative of killing his friend and charge. His good intentions are evidenced in his final words to Lennie. He encourages Lennie to think about the ranch they will have together, and declares that "'Ever'body gonna be nice to you. Ain't gonna be no more trouble. Nobody gonna hurt nobody nor steal from 'em.'" (Chapter 6). Slim, who also works on the farm alongside them, assures George that he did what he had to do.