In general, castling is a good thing. In this case, and in retrospect, it was unwise. Carlsens pieces were aiming at the king side so further development and th

In general, castling is a good thing. In this case, and in retrospect, it was unwise. Carlsens pieces were aiming at the king side so further development and then castling queen side would have made more sense. I think Gates' first mistake was 3. Bd3. It blocks the d-pawn and the bishop isn't very active at Bd3. The computer gives white a small advantage after 2. .. d5 but a disadvantage after Bd3. It prefers to just take the pawn. With low depth the computer also plays Gates 4th to 6th move. So despite the threads on the king side castling seems possible. 6. h3 is not recommended but it thinks Blakcks response 7 .. Ne5 is a blunder. However, with his last move, allowing the mate, Gates really blunders. If he would have played Re1 instead the computer gives an advantage of almost 3 pawns. Note: the computer was Stockfish