In the final chapter of John Steinbeck's 1937 novel Of Mice and Men, our two friends George and Lennie meet their final challenge after Lennie accidentally kills Curley's wife. George and Candy realize that Curley and the rest of the men will want to kill Lennie. George does not want Lennie to be treated brutally by Curley and the other men, so he does what Steinbeck has prepared the audience for ever since the moment that Carlson shot Candy's old dog with the Luger. Thus, George himself gets Carlson's Luger and goes of with the men in search of Lennie.
Before George arrives, the audience hears Lennie's conversations with himself. They hear the critical voices inside Lennie's head, as the man chastises himself for his past actions. Soon, however, George arrives and tells Lennie once again about the friendship they share and their dreams for the "little place" that they will have together. It is with thoughts in his mind of their own personal utopia that Lennie dies, killed by his friend.
Thus, I would say that Steinbeck shows compassion for Lennie by not allowing him to be killed by a lynch mob and by not allowing him to die with his final thoughts being one's of self-criticism. Lennie dies at the hands of his best friend, who brought about Lennie's death as swiftly as he possibly could and who reminded him of their friendship and their dream up until the very end of his life. The novel ends with Slim declaring that George had no other choice:
Slim said, “You hadda, George. I swear you hadda. Come on with me.”