Growing up, I watched Saturday morning television cartoons in which a character was making a decision. On one shoulder an angel hovered, saying, "Do the right thing!" But on the other shoulder perched a devil urging the character to do the wrong thing. You already know what happened: as the angel looked increasingly anxious, the cartoon character chose to do the wrong thing.
Paul's Galatians didn't watch TV cartoons, but they probably had a similar model of decision making.