A defender that's holding two jobs at once is really doing neither. Deflection means forcing that overworked piece to commit to one job, often by capturing one of the things it defends, even at the cost of your own material, so that the other thing it was guarding collapses.
The classic setup is a back rank: one defender guards the mating square, and a sacrifice drags it away. Don't be afraid of the price tag on the first move. If the follow-up is checkmate, you can pay anything, even the queen.
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Black's queen on d8 is the only piece guarding the rook on e8, and e8 is the square where White's rook wants to deliver mate.
Black's queen is overworked. Sacrifice your queen to prove it.
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