what is important about the title

John Steinbeck takes the title of this novella from the poem "To a Mouse [on turning her up in her nest with the plough]," written by Scottish poet Robert Burns in 1785. In the poem, the speaker has accidentally turned up a mouse’s nest with his plough, and takes the opportunity to wonder at man’s separation from the world of animals. Still, the speaker thinks both mice and men suffer from being mortal, so no matter how different "thinking men" and "unthinking animals" seem, they really aren’t that different after all – everybody suffers in the end. This thought isn’t too far off from what ends up happening to our "thinking man" (George) and his "unthinking friend" (Lennie).