And it's "safe" that Sam says is why he went to Stanford, isn't it -- not normal, the word he uses is "safe." I think this is one of those things running through the show, and of course the whole Winchester story makes it clear that ignorance is no protection. If it were, Mary would still be alive and maybe Jess as well.

But admitting that means, I think, coming a little too close to the idea that if John had known what was coming, he could have kept Mary safe. Which I think John believes even though he suspects it isn't true.