In Carlsen v Ivanchuk Game 1 it wasn't immediately obvious to me why Ivanchuk resigned. However, he is two pawns down with no compensation and White's a4 rook is going a2, d2, d7. Carlsen played so many moves I would have rejected, e.g. e4-e5 allowing Black the d5 outpost for a knight, previously putting the f1 rook to c1 with the a1 rook and b1 knight still at home. Also happily leaving a rook hemmed in on a4 after b2-b4.
However, his aggressive e5-e6 dissipated much of his advantage, according to the engine. But then it's encouraging for us amateurs to see how often GMs fail to find the best moves, especially in tactical situations, and Ivanchuk still couldn't find a defence against that sub-optimal e5-e6.