Why is Candy lonely in Of Mice And Men?

Candy could be considered lonely after the death of his dog. Before that he seems relatively happy and, in fact, is quite gregarious in chapter two when George and Lennie first enter the bunkhouse of the ranch. He goes on about the other characters and describes the Boss, Slim, Crooks, Curley and Curley's wife. He even gossips with George, telling the story about the glove on Curley's left hand which is full of vaseline so...

Candy could be considered lonely after the death of his dog. Before that he seems relatively happy and, in fact, is quite gregarious in chapter two when George and Lennie first enter the bunkhouse of the ranch. He goes on about the other characters and describes the Boss, Slim, Crooks, Curley and Curley's wife. He even gossips with George, telling the story about the glove on Curley's left hand which is full of vaseline so he can keep "that hand soft for his wife."

It is not until chapter three that Candy's life turns lonely. Carlson, a laborer on the ranch, believes that Candy's dog is too old and decrepit. He suggests that Candy shoot it to put it out of its misery. Candy can't do it and, because Slim gives Carlson the approval, the man takes Candy's dog and kills it. Obviously, the dog was Candy's best friend and the loss throws him into depression. Steinbeck describes Candy right after the men hear the shot that kills the dog:

For a moment he continued to stare at the ceiling. Then he rolled slowly over and faced the wall and lay silent. 

Candy's loneliness over the loss of his dog is short lived as he becomes part of George's and Lennie's plan to get their own farm. In fact, Candy makes the dream seem almost possible because he has saved $300 which he will contribute to the price of the property George can buy. The three men believe that one day they will up and leave the ranch and go live on their own "little piece of land."

In the end, however, Candy is plunged back into despair and loneliness after he discovers Lennie has killed Curley's wife. The dream is shattered. He poignantly communicates his feelings over the loss at the end of chapter five:

“You done it, di’n’t you? I s’pose you’re glad. Ever’body knowed you’d mess things up. You wasn’t no good. You ain’t no good now, you lousy tart.” He sniveled, and his voice shook. “I could of hoed in the garden and washed dishes for them guys.” He paused, and then went on in a singsong. And he repeated the old words: “If they was a circus or a baseball game . . . . we would of went to her . . . . jus’ said ‘ta hell with work,’ an’ went to her. Never ast nobody’s say so. An’ they’d of been a pig and chickens . . . . an’ in the winter . . . . the little fat stove . . . . an’ the rain comin’ . . . . an’ us jes’ settin’ there.” His eyes blinded with tears and he turned and went weakly out of the barn, and he rubbed his bristly whiskers with his wrist stump. 

The reader may assume that Candy lived out the remainder of his life a lonely man swamping out the bunkhouse on the ranch.