Of Mice and Men by John Steinbeck, traces the tragic consequences which can result from well-meaning intentions. George feels responsible for Lennie, a simple-minded migrant worker who is totally reliant on him to the point where George feels it is necessary, ultimately, to kill Lennie to protect him from himself and the lynch mob that is approaching. As Slim points out to George, "A guy got to sometimes." Slim understands George's predicament and the impossible situation that has resulted from Lennie having accidentally killed Curley's wife. This is a prime example of external conflict in the novel, as George recognizes the threat from Curley's mob and also of George's inner conflict as he wants to protect his friend and feels duty-bound to do so but ironically, as he is unable to do that, he must make a decision to end Lennie's life.
George's inner conflict arises from his feelings of duty and responsibility which do sometimes overwhelm him to the point where even Lennie, on occasion, recognizes Geroge's turmoil such as when he says, "I'll go right off in the hills an' find a cave if you don' want me." Lennie has no concept of consequences, however, and quickly moves on to discuss their dream of a farm and the rabbits that Lennie imagines he will be looking after. George will, of course, never abandon his friend despite sometimes imagining how much easier his life would be without Lennie.
"God, you're a lot of trouble," said George. "I could get along so easy and so nice if I didn't have you on my tail. I could live so easy and maybe have a girl."
George and Lennie have been thrust into a world which is very difficult for a migrant worker and it is necessity that first categorizes their friendship. However, George realizes the extent of Lennie's dependence on him when he tells him to jump into the river and, because of the complete trust that Lennie has in George, he unquestioningly jumps in and it becomes necessary for George to save him from drowning.
With or without Lennie, George's life would be hard and his dream of a tending his own farm is kept alive by Lennie. This further reveals George's inner conflict as he is also dependent on Lennie in order to have real purpose in his life.