Flannery O’Connor once described the contradictory desires that afflict all of us with characteristic simplicity. “Free will does not mean one will,” she wrote, “but many wills conflicting in one man.” The existence of appealing alternatives, after all, is what makes free will free: What would choice be without inner debate? We’re torn between staying faithful and that alluring man or woman across the room. We can’t resist the red velvet cake despite having sworn to keep our calories down. We buy a leather jacket on impulse, even though we know we’ll need the money for other things.