Imagine it is a simple as taking away Dak's first read and he panics. And yet, the Cowboys won 12 games.
I have no doubt Dak is tight in big games. He looked nervous warming up and in the first huddle. That is a problem for him and the team. And I assume the entire offense picks up on his nerves. It seems when Dak get tight like that he stares down his receivers, his mind slows down and he can't make quick decisions. I posted yesterday that Dak was dumping the ball of to the RB and TE in the flat too late which resulted in completions but no yards. He has to get the ball out there before the defense can react giving the receivers a chance to run for a few yards. Even 5 yards is better than nothing. Dak gets brain lock when he is tight too.
Look at Dak to start the game and until the game was out of hand. He was awful. No yards, two INTs, including a pick 6, and 0 points. The Packers go up 27-0 and all of a sudden Dak finds his rhythm. He found his rhythm because when the game was out of hand the pressure was off, the defense probably relaxed a bit too. This is why I would not fire McCarthy. He is doing the best he can with the QB he was dealt.