He was abandoned, he needs to care for someone and be loved. Lennie dreams of taking care of soft, innocent, rabbits the way a mother yearn to bond with her baby. It is his outer strength that belies his nature, and serves to bring on his demise. George is the other main character in this small novel. George is the role model, father figure, dreamer that sets a path of hope out for not only Lennie, but himself as well.
Society takes so much for granted.
George is a hard working migrant laborer that has spent his sweat and time both caring for Lennie and keeping his dream alive as well. George and Lennie set out to work as migrant workers and ranch hands to get some money together to make their dream come true. Steinbeck foreshadows their troubles throughout the book from the death of a small mouse in the first portion of the book. This is a theme that is repeated often. Death of youth, death of innocence, death of dreams etc.