Hopes and dreams are important parts to the characterizations in Steinbeck's work. Each of the main characters is driven by their hopes and dreams. They are important because they provide motivation and a sense of animation to each of their being. When these hopes and dreams are gone, it becomes clear that a part of their humanity goes, also.
Lennie and George are driven by their hopes and dreams of owning a farm. For Lennie, this immediately translates into "tending the rabbits." For George, this becomes the idea that they can own "a piece of land" and control it for themselves. Such hopes and dreams are important to George and Lennie because it provides motivation to them and helps them endure challenging times. The ability to hope and dream is of vital importance to their being.
Hoping and dreaming is how Candy can be best described in his dreams of sharing in the hope of George and Lennie. Candy is motivated by his sharing in their hopes and dreams. Candy is broken when he finds Curley's wife's body because it marks the end of his dreams. Interestingly enough, Curley's wife's death is caused, to an extent, by her own hoping and dreaming. In detailing her dreams and potential chance at stardom to Lennie, she is encouraged to have him feel her hair, bringing about the fatality. Candy's cursing of the corpse is a statement of how important hoping and dreaming is to the individual in Steinbeck's world.
In the end, characters in Steinbeck's novel are ones that find hoping and dreaming important. When this ability to hope and dream goes away, some level of the characters' humanity goes with it. In this, Steinbeck makes clear that individuals who lose the ability to hope and dream die a little bit from an emotional point of view.
Both are important because they decorate the life and mankind easily runs on their tracks. If they are violated,the life will be meaningless and our existence will be perished.