How and why does the dream change throughout the book? What makes it stronger or weaker?

George and Lennie have no way of realizing their dream until old Candy overhears them talking about it. Candy actually has most of the money for the men to buy the farm so the dream changes to include Candy. Later, Crooks even asks about it but declines after Curley's wife humiliates him. After Lennie kills Curley's wife, George knows the dream is dead.