I will try and not put out spoilers, but I am afraid I must for explanations sake, so if you were going to read this post then read the book, don't read this post, instead, read the book, then this post.
The book,
Of Mice and Men, is the story of two men's struggles to obtain a decent life in a time where that would seem impossible to anyone else. The books title comes from a poem called
To A Mouse, by Robert Burns, which goes like "The best-laid plans of mice and men/often go awry". This also happens to be the theme of the book, which goes about from beginning to end mapping out this statement ever so intricately and cunningly. The books theme of failure to carry out ones best plans is shown in this book through foreshadowing, character development and sybolism.
The book uses foreshadowing in a few different places, but they all centralize around the character Lennie Small. Starting off in the beginning, it first shows Lennie killing a mouse by over petting it, then we learn about an incident in the town of Weed where he got himself and George, his companion, run out of town by panicking when he went to feel a girls dress and she calls out "rape", making him instinctively grab on and hold onto the girls dress. In other words, it is showing that he likes feeling and petting things that are soft and pretty, which leads up to him petting another characters hair in the end of the book, causing her to panic, which causes him to panic, which makes him hold on so tight to where the characters panicked flailing causes him to accidentally crack her neck, killing her.
The next literary device has to do with the other main character, George. He really develops as a character throughout the book, rather slowly in the beginning, but he really is changed by the end of the book. He starts out in an almost hopeful state, aided by Lennie, who makes him repeat their goal of a home with rabbits and land and other livestock. He then progresses into a very hopeful state midway through their stay at the ranch, after they go over the story and their plans on how to get there multiple times. He then takes a turn for the worst and changes exponentially, changing into a person that is in an almost hopeless state, but almost dumbstruck that he didn't realize that the events that happened would have happened anyways earlier at the end of the book. But he is always looking out for Lennie, which could also disprove the statement of the change of character.
The last literary device in this book is symbolism. I think that the biggest symbol in the book is the rabbit. It shows up in every chapter that I can remember, and is usually symbolic of the ideal lifestyle that they, or maybe just Lennie wanted. Towards the end of the book though, it turns to a more sinister symbol, telling Lennie about how bad of a person he is and how George doesn't need him. I see it as a symbol of what the title of the book was derived from. I see the rabbit as the great plan all laid out, then going awry like every great plan does. Also, in my experience at least, the rabbit has always been the thing to escape anyones grasp, which supports the theory of what it symbolizes. I also think that Lennie and George's relationship is symbolic of the nature of business. The smaller but more clever one manipulates the larger less clever one into doing his bidding and remaining controlled, but once the less clever one gets out of control, be it by his own will or not, the more clever one will have to do away with the less clever one in anyway necessary, similar to many Incredible Hulk story lines.
Overall, the theme of this book, how no good plan ever goes as planned, is brought out of the book and into the readers mind through various different literary techniques such as foreshadowing, character development, and symbolism. The book seems to be very loosely based on the poem that the title was named from, and if you read the poem, it could also be seen as a literary device.