Figure 3.1.14.4[Black to move]

Now a defensive use of our current idea, and in a horizontal setting. Black is ahead a piece. He has to address White’s threats against his knight and bishop. How? With offense: Black has a bishop on the eighth rank and can move his queen behind it with Qd8. That move creates the kernel of a discovered attack against White's queen. To make the threat really interesting the bishop would need somewhere good to go. Can it reach White’s king? Not quite; it can move to a6, though, at which point it is aimed at—the threatened knight. Now the defensive idea comes together: if Black plays Qd8 and White then plays KxN, as he now threatens to do, Black would be able to win the queen with Ba6+. Odd as it may seem, by moving his queen to d8 Black thus defends his knight on e2: he creates a discovered attack that will be unleashed if his knight is taken.