Candy is motivated to contribute to George and Lennie's venture of owning a farm because he is growing older, has lost his faithful dog and friend and is now isolated, and may soon lose his job sweeping out the bunkhouses.
The old, stoop-shouldered man, Candy, does little but push a broom and clean the bunkhouse since he is too old and crippled; added to this condition, Candy has lost a hand in a farm accident. Therefore, he is worried that he will suffer a similar fate to his old dog, or at least, be alone.
Further, when Candy overhears George and Lennie talking about the farm that they hope to have, he eagerly asks them, "You know where's a place like that?" George is at first suspicious, but Candy expresses his worry that he is not "much good with on'y one hand," and he adds that he received money for his accident and can contribute over three hundred dollars. Certainly, at the prospect of a real home and fraternity with men rather than isolation, Candy eagerly asks to participate.