SPOILER ALERT!!! GO WATCH THIS MOVIE FIRST, THEN COME BACK
Our nameless main character finally made it to the top. He only made one mistake, he stole someone's girlfriend. As the narration ends and it becomes "present time", rule #1 comes back to bite him. Don't mess with another man's girl. You don't get to see good unexpected endings like this much in Hollywood anymore.
You're born, you take shit, move up, take less shit. There will always be a successor. Welcome to the Layer Cake.