It is obvious from the beginning of the novel that Lennie is in some way mentally disabled, and has the mind and actions of a child, the first time that a character mentions this is Slim, who remarks that Lennie is 'Jes like a kid', Curley's wife also point out that he is 'jus' like a big baby'. It is obvious to the reader of Lennie's mental ability by the way he speaks, as he has a definite speech impediment. By having Lennie be described as like a child and by his actions being like a child, it effectively creates sympathy for the character from the readers. This is because it is always easy for a reader to feel sympathetic towards a person with mental difficulties as you can understand how challenging it must be in their situation.
I don't think Steinbeck creates sympathy for George a such... There's the theme of the American Dream, and the reader's feel sympathy for George because he keeps telling Lennie about the dream so much he believes it himself now. It's such a small thing that makes him so happy, and it's his only hope so the reader feels sorry for George and how hard his life is. When George shoots Lennie the reader feels sympathy because George has been travelling with Lennie for years, and he has to shoot him. It's a sad but necessary action for George, but it doesn't mean that te audience doesn't empathise with George for shooting his best friend. Without Lennie there, George is just a lonely migrant worker, with no ties to anybody or anywhere, just like the others. Before; "you got me and I got you" Lennie says, but when Lennie's gone, so is his feeling of having a friend. It's not much. It's the loneliness really that creates sympathy for George. Crooks
Crooks brings into perspective the loneliness experienced by all the characters in "Of Mice and Men" by saying (p. 77) "Sure, you could play horseshoes till it got dark, but then you got to read books. Books ain't no good. A guy needs someone - to be near him. A guys goes...