Where does White have the makings of a discovery? On both the d-file and e-file, where his knights mask his queen and rook respectively. Look for targets for the masked pieces and you see that on the d-file there is a loose Black knight. All White needs is a good threat for his knight to make as it uncloaks the queen. You might first look at checks and find Ne6; but then what? The knight is lost after f7xN, and then if White plays QxN Black has e6xQ—not good! But then look at the knight’s other possible squares and notice Nc6: a move that both attacks Black’s queen and keeps the White knight safe. Black moves his queen, and White has QxN for free on his next move.