When we first meet Lennie and George, we almost can't tell them apart: "Both were dressed in denim trousers and in denim coats with brass buttons. Both wore black, shapeless hats and both carried tight blanket rolls slung over their shoulders" (1.4). They're two itinerant farmworkers, looking for work wherever they can. From a distance, there's nothing to tell either apart. But when we get closer, we see that this isn't a relationship of equals:
If this reminds you of a kid imitating his dad, then you're on the right track: from these few sentences, we know that something is seriously wrong with Lennie. Like a kid, he mournfully wishes for ketchup to put on his beans; like a kid, he demands a bedtime story—even when he knows it all himself: "No…you tell it. It ain't the same if I tell it. Go on…George. How I get to tend the rabbits" (1.121).