“They don’t need you. Not like you need them.”

—Yellow-Eyed Demon, “Devil’s Trap” (1-22)

The day little Sammy Winchester learned there was no such thing as Santa Claus, his big brother tried to soften the blow with another revelation: “We have the coolest dad in the world. He’s a superhero” (“A Very Supernatural Christmas,” 3-8). Dean was just a boy himself when he issued that naÏve affirmation, but it wasn’t a sentiment he’d be quick to outgrow. That unshakable faith in his father became so central to Dean’s personal worldview, so essential to his sense of well-being, that it constituted a lifeline for him, keeping the powerful currents and crashing waves that enervate mortal existence from pulling him away and dragging him under. But when John made his deal with the devil in an effort to save his eldest son, he severed that lifeline. Dean was left feeling abandoned and disconcertedly betrayed. It seems likely he would have felt the same no matter what John’s bargain had been, even if John had forgone the additional cruel blow of the “Sam bombshell”… If the devotedly vigilant big brother could not save the youngest Winchester, Dean would have to kill him. Kill Sammy. On the surface of it, you had to wonder what was going through crazy John’s head when he extracted that heartbreaking promise.

Perhaps, though, there was a method to his madness.

That’s not how it appeared at first, of course. In the initial weeks after their father’s death, Sam spent a  …