The description that can be made of the "human condition" as it is illustrated in the story shows two men with a huge dream, whose lives are eternally at the mercy of their circumstance.
These two men, George and Lennie, are consistently surrounded by all the obstacles and limitations that prevent them from achieving their one dream of living in a farm on their own. Not only do they deal daily with illiterate people with pessimistic attitudes, but they are constantly struggling for a way to make the money to go after their dream.
Furthermore, George and Lennie must put up with a hard farm job under the supervision of a bad man, who is Curley. Curley is the type of boss that is capable of nearly anything if he feels threatened by anybody. Therefore, one must imagine the pressure of working for Curley in a place as depressive as Soledad. Soledad, in Spanish, means "loneliness", or "isolation". This is the atmosphere in the lives of George and Lennie.
Although George and Lennie are basically two decent individuals who simply cannot make their plans come to live, they have yet one more problem: Lennie's behavior. When Lennie, in his immense strength, accidentally kills Curley's wife, everything that the two men hoped and wished for comes crumbling down.
As George prepares to kill Lennie before the lynch mob gets Lennie and tortures him, we realize how inhumane the lives of George and Lennie have really been. No hope, no money, no help, not even support either moral or financial of any kind (except for Candy) comes their way. However small their hopes are, they continue to be eliminated one by one.
Hence, the inhumanity is demonstrated in how George and Lennie's conditions of life are so entirely dependent on fate. And fate wins all the time.