Really hard to break it all down to any one thing.
As I see it, it's a culmination of preparation, mental, AND physical conditioning, speed reading, and instantaneous reaction to plays that sometimes don't go as designed.
I think that's why I think that the "Remarkable Russell Wilson" is in the discussion when people are talking about "Elite Quarterbacks"
He doesn't put up the gaudy numbers that a lot of the greats are touted for, but then again, he isn't asked to, and he plays within the parameters that asked of him, takes care of the ball, and that is why in just two Years, he led the Seahawks to a WORLD CHAMPIONSHIP.