Another study in destabilizing a pawn in the center. The White pawn on e5 looks secure; it is attacked by both Black knights, but defended by White’s queen and knight. Yet those White guardians of the e-pawn are themselves attacked by Black’s queen. Is there some way for Black to cause an exchange that allows the pawn to be taken? An initial unappealing thought is QxN, since after the recapture QxQ both White guards have been eliminated—but of course this loses the queen for a knight and a pawn, which is no good. If only the positions of White’s queen and knight were reversed; then Black could play the straight trade QxQ, removing a guard at no cost. Yet in that fantasy lies a solution: Black plays Nc6xe5, and after White recaptures NxN, Black then is able to play QxQ. After White recaptures h2xQ, Black still has time for NxN, again picking up a pawn and a positional advantage: White’s pawn in the center has been eliminated, and the defenses in front of his king have been gutted.
Notice a nifty sidelight here. White could reply to Black’s initial capture with Nb1-d2; the move adds a defender to the f3 knight and also attacks the Black queen in its current position, leaving it nowhere safe to stay on the third rank. It’s almost good, but Black has a riposte: Ne5xN+. Since it’s a check, White has no time to play NxQ; he has to capture Black’s knight. Black holds on to the pawn. But it's still important to see the idea of Nb1-d2, as it illustrates again a recurrent theme. Do not take for granted that your opponent will respond to your capture with an immediate recapture. He may be able to play a zwischenzug—German for an “in between” move inserted before a recapture you had been expecting—that throws off your plans. Here Black nevertheless succeeds by countering with a different recurring principle: the priority of check.
Incidentally, it would be a mistake for Black to start the sequence by capturing with the knight on g6; the pawn behind it on g7 is loose and gets taken by White’s queen. Pawns on the second rank often get left loose, and they make fine snacks for queens and rooks.