Take stock of White’s threats. (a) His queen attacks Black’s knight on c6, which is guarded by a pawn and by the knight on d7. (b) His queen also attacks Black’s bishop on a5, which is protected by the knight on c6. (c) His bishop on a3 attacks the knight on e7, which is guarded by the knight on c6. The first thing is to see all those threats; the second is to ask how they relate to each other. The key point: White attacks two pieces guarded only by the knight on c6. He therefore plays 1. BxNe7, obviously preferring to start by offering up his bishop rather than his queen. If Black recaptures NxB, White has QxB, winning a piece in any event. (Black can get a little something back by replying to 1. BxNe7 with Ba5xc3, threatening White's rooks. After White recaptures with the knight from b1, Black can make his own recapture NxBe7 without exposing any of his other pieces to fresh capture. In effect he picked up a pawn to help mitigate his loss of a piece.)

Again, a shorthand route to the same result is to see that White’s queen attacks Black’s bishop at a5, but is prevented from taking it by the knight on c6; to ask what else that knight protects, and then be led to the knight on e7; and thus to play BxN, putting Black to the choice of forfeiting his knight or recapturing and then losing his bishop.