A FORCED MATE OF 51 MOVES. There was a computer program called “Stockfish” running in real time on a supercomputer during the championship games. Oliver Roeder points out that in the second game, Stockfish found a forced checkmate of 51 (!) moves for Carlsen on his 62nd move. Carlsen, understandably did not see it. Later, Stockfish found a forced checkmate of 22 moves for Carlsen on his 73rd move. Again, Carlsen understandably did not find it. The game ended in a draw on the 84th move.
These unseen combinations illustrate the advantage that a computer has over humans. Human chess games often turn on the ability to calculate rapidly. However, calculating 25 to 50 moves ahead (over and over) in the time limits that apply in championship games is not something humans can do consistently.