Tactics & checkmates
Deflection
Deflection forces or tempts an enemy piece to abandon an important defensive duty. The real target is often not the diverted piece itself, but the square or piece it will no longer protect.
A practical example
A rook guards a back-rank mating square. A sacrifice attacks that rook in a way that taking it abandons the square. If the rook accepts and there is no other defence, the mating attack can break through.
A common mistake
Assuming the opponent must accept a sacrifice. If they can decline it while stopping your threat, the combination is not forced. A second defender may also prevent the idea.
Try this in your next review
For each defender, ask what it protects. Look for a move that draws it away from that duty, then calculate the line where the opponent declines the sacrifice.