Steinbeck examines the themes of isolation, trust, friendship, and fear throughout the novella Of Mice and Men. In a conversation between George and Slim, Slim says,

"Ain't many guys travel around together...I don't know why. Maybe ever'body in the whole damn world is scared of each other" (Steinbeck, 17).

Slim is essentially saying that the majority of individuals in the world choose to reject close relationships because people fear that others will harm them in some way or form. During the Great Depression, many Americans lost their jobs and were forced to contend with one another in order to survive. In this hostile atmosphere, individuals became wary of one another and often feared their neighbors.

Steinbeck expands on Slim's comment by exploring the nature of Curley, George, and Lennie. All three characters fear other individuals on the farm throughout the novella. Curley fears that each of the workers, most notably Slim, will attempt to sleep with his wife. His bravado is an attempt to conceal his inner turmoil. George fears that he will be fired from the ranch, leaving him jobless in a competitive environment. He fears that Curley's wife will ruin his current situation. Lennie, who would be helpless without his only friend and guardian, fears that George will leave him.

One of the themes of the story is that people do not trust one another, and most people are alone.

Slim is surprised when he learns that George and Lennie are traveling together.

Slim looked through George and beyond him. “Ain’t many guys travel around together,” he mused. “I don’t know why. Maybe ever’body in the whole damn world is scared of each other.” (ch 2)

George and Lennie have certainly discovered a lack of trust and understanding.  They were  run out of weed when Lennie had an altercation with a girl who mistook his childlike behavior as predatory.

Curley is an example of the behavior that they are worried about.  He does not trust anyone, and automatically assumes the worst.

His eyes passed over the new men and he stopped. He glanced coldly at George and then at Lennie. His arms gradually bent at the elbows and his hands closed into fists. He stiffened and went into a slight crouch. His glance was at once calculating and pugnacious. Lennie squirmed under the look and shifted his feet nervously. Curley stepped gingerly close to him. (ch 2)

Curley is ready for a fight at first sight.  He assumes Lennie is a threat because of his large size, and is suspicious of both of them.  He certainly exemplifies Slim’s words.  He is afraid of everyone.