Unique?

I do not understand how we are different and the same. There are seven billion men waiting to be blamed, Yet somehow each one is different. No man ever steps in the same river twice, For its not the same river. But a river is a body of water And so are lakes And oceans of saltwater. The Fishes think they are all rather nice, For they've never cared before; Yet somehow each one is different. And he's not the same man. But a man is a human On Earth On that same river stomping. And no man is truly different because no men want to change; Yet somehow each one is different, And everyone's the same.