Deflection works by attacking a piece that serves a dual purpose: defending a key square and performing another role. When the piece is forced to deal with the new threat, it can no longer maintain its defensive function, allowing the attacker to exploit the abandoned target.
A common example is deflecting a rook that is guarding the back rank. If the rook is forced to capture a piece on a different square, the back rank becomes undefended, potentially allowing a back-rank mate. Similarly, deflecting a queen from defending a critical square can open up mating possibilities.
Deflection often works in combination with other tactics like decoy and overloading. When you notice that a single piece is holding the opponent's position together, look for ways to force that piece away from its critical assignment. Sacrifices are frequently used to achieve deflection.