Steinbeck might be making both characters similar and yet fundamentally different to display the paths that individuals may take in times of economic challenge.  The condition in which both characters find themselves is one of challenging constraints from a material point of view.  Essentially, Steinbeck is suggesting that even in such a state one has a conscious choice of how they wish to be and how to carry themselves.  In Chapter 3, George talks to Slim about how he used to tease and torment Lennie and yet Lennie demonstrated the greatest in loyalty and the capacity for goodness despite such harsh treatment.  This fostered a sense of change in George.  George's compassion and care for Lennie even though he is a "nuisance" is something that shows how individuals can possess a capacity for caring and understanding even though there might be economically challenging conditions that surround them.  For Curley, there is no such compassion.  Curley is a bitter and hardened individual who can only accept the conditions of his own failed condition as a boxer as part of what defines his being.  Whereas George has transcended to a great extent his own temporality,  Curley has succumbed to it.  It is here in which Steinbeck is suggesting that individuals have the capacity for change and must activate it over the course of their own being despite the temporal conditions around them.  It is this state that defines who we are and what we are to be.