People are shown as having dreams that are fated not to come true, most obviously George and Lennie's dream of owning their own land.
Of Mice and Men
There is a wider dream of freedom and independence that is also shown as fated never to happen, a dream shared by many Americans.
Most of the characters either face loneliness (Curley's wife, Crooks, Candy), fear it (George and Lennie) or are lonely without realising it (Curley).
The novel suggests that humans are fragile creatures not really in control of their lives who have to snatch joy while they can.
The novel protests about the treatment of workers, the treatment of old age and about racial prejudice.