what is the relation of mice with men in this novel?

John Steinbeck takes the title of his little novel or novella from the poem "To a Mouse (on turning her up in her nest with the plough)." It was written by Scottish poet Robert Burns in 1785. The idea of the poem ( and the book) is that despite all our crazy plans, men and all animals (yes mice included) are subject to the harsh realities of life, including death.