The one where they send Dean back in time.

And that doesn't tell us why Lucifer insists that is was always meant to be Sam. Or why Michael chose Dean. Is it Dean because it was Sam? Was it "destined" that Mary would make the deal? Is it a Winchester-Campbell thing?


What I'm saying is, the plot is semi-clear on why Sam got demon-blood dripped in him. It is not clear why both the brothers are involved in the larger arc, nor is it clear why both the brothers are being pegged in retrospect by the angels as being the people who would be the vessels of the larger arc. Why them? Would any brothers with these particular Daddy issues have done? Are they the favourite because John went nutso with vengeance?