In Of Mice and Men what message does John Steinbeck emit about dreams and goals?

Steinbeck's message about dreams in Of Mice and Men represents the general theme of American Modern Literature--disillusionment (especially with the unreachable American Dream). Almost all of the characters in the novella demonstrate this theme of unreachable dreams/goals. Here are some specific examples:

1. George and Lennie--The main companions simply want a place of their own where they don't have to worry about people driving them away or bossing them around.  They want to leave loneliness and shiftlessness behind and have a permanent place.  Of course, not a single part of this dream comes true for George and Lennie.  They come so close to obtaining the farm, but all is lost when George must kill Lennie to prevent Curley from getting to him.  George is left alone and hopeless.

2. Candy--Candy simply wants to be needed and useful. He jumps at the opportunity to go in on the farm dream with George and Lennie, but all that is lost when Lennie kills Curley's Wife.  He, too, is left without his farm, without a friend, and without even a dog.

3. Curley's Wife--Curley's Wife dreams of attention and praise.  She wants to be a movie star but marries Curley instead.  She is stuck in a loveless, abusive marriage with no way out.  She dies never realizing her dream.

4. Crooks--Crooks wants equality and companionship.  He first agrees to go in on the farm dream with Candy, George and Lennie, but then backs out when Curley's Wife threatens him with false accusations. At the novella's end, he is left with his isolation and books.

Steinbeck's own disillusionment with dreams and goals is understandable especially since he concerned himself with the plight of Okies and migrant workers during the Great Depression.  His message is not unlike Fitzgerald's portrayal of unreachable or corrupted dreams in The Great Gatsby.