Candy has not been able do a great many things. In the context of the novel, it becomes clear that Candy has never really been in a setting where he was treated as an equal. Candy has never been a part of a setting where his voice was validated. When Candy tells George and Lennie that he would like to be a part of their dream, this becomes clear:
I got hurt four year ago...They’ll can me purty soon. Jus’ as soon as I can’t swamp out no bunk houses they’ll put me on the county. Maybe if I give you guys my money, you’ll let me hoe in the garden even after I ain’t no good at it. An’ I’ll wash dishes an’ little chicken stuff like that. But I’ll be on our own place, an’ I’ll be let to work on our own place.
The idea of "on our own place" is appealing to Candy because it represents a sense of empowerment that he had never experienced. His role on the ranch is marginal, and given that he obtained it as a result of the loss of his arm, it becomes evident that Candy has not been in a situation where he is seen as an equal. He recognizes this dream when he sees that he can be a part of the vision that George and Lennie share. Candy has never been able to accomplish a dream where his own happiness is evident. For just a brief moment, he is able to envision this with George and Lennie. Given the yearning and sense of longing that is the undertone to Candy's speaking in this part of the text, he has never been able to do this. It is for this reason that he is both so very excited at its prospect and so emotionally crushed by the end of the novel.