Harsher in Hindsight: In On A Pale Horse, Lachesis defends Fate's meddling in Zane's life by saying that "all mankind will be damned" if they don't meddle. Come For Love of Evil, we learn that Satan doesn't actually intend any such thing. Quite the opposite actually. His bid to claim God's power is motivated by a desire to stop people from being damned unfairly. The idea that the forces of Good may have actually been preventing a desirable outcome (and unwittingly subjecting countless innocent souls to damnation) by their interference is some pretty serious Fridge Horror.
Idiot Plot: The resolution of the plot in ...And Eternity only happens the way it does because Satan and the Incarnations are adhering to rules that are expressly referred to as a game. Every person involved in the system (the Incarnations except for God, who's effectively out of commission, plus Luna, Jolie and Orlene) has the same objective: dethrone God and fix the rules for the afterlife. Furthermore, they agree on what fixes need to be made. Nonetheless, Satan tries to stop the other side's plan and force them to capitulate to his leadership, not because his ego is on the line, but because he's supposed to play the game.