I've done some pretty rotten things in my life, but I don't think I've ever been the first person to do one of those rotten things. I wonder what it was like for Cain when he realized the magnitude of his sin. It's hard to believe that humanity took such a dive in such a small amount of time: in a matter of years, the first human beings moved from intimate connection with God to total disobedience. The words of God to Cain are telling, too: "sin is crouching at the door. Its desire is for you, but you must rule over it." Cain had a choice. He was not predestined to sin, nor was he forced into it involuntarily. No, Cain chose his path in much the same way that we do.
The truly encouraging part of this reading comes when God decides to flood the earth. I don't say that to be facetious; I really believe it's encouraging. God could have ended the story here, but He opted to go down another road. He would offer redemption another way, and that redemption would come in the form of Jesus Christ, incarnated on earth, several centuries later. We know that Jesus was alive at this point (see John 1:1)… He just hadn't yet shown up on the radar screen of humanity. Hope is rising… it's just a matter of time.