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Protecting a piece is insufficient, if the protector can be forced away, because it has to capture somewhere else, leaving the piece unprotected.
Sometimes a protector has more than one task. It has to protect two pieces, or a piece and another square. Such a protector is called "overloaded", if after performing one of the tasks, it is deflected away from doing the other.
The black rook on c8 is protecting the queen on c7, and the rook on a8.
It is overloaded, and White can win material with the deflection Qxc7.
After Black recaptures with Rxc7, the rook is deflected away from protecting the other rook on a8, and White wins with Rxa8.
Sometimes a deflection can involve a temporary sacrifice, as in the following example:
The queen on c6 is protecting the bishop on g2, and the rook on c5.
It is overloaded, and White can win material with the deflection Rxg2, temporarily sacrificing an exchange.
After the queen recaptures with Qxg2, it is deflected away from protecting the rook on c5, and White can capture that with Qxc5.
The investment was a good one, in the end Black has won the bishop on g2, and is two pawns up in a winning endgame.
Sometimes deflections can be a bit more complicated:
The rook on c7 is guarding the square e7 against the knight fork Ne7+.
However, White can play Ne7+ anyway, as it turns out that after Rxe7, the rook has been deflected away from the c-file.
White can win material with Rxc8+.
When you are attacking a protected piece, always think about ways to remove the defence.
If a protector has more than one task, always check if a deflection is possible.
There are various ways to remove the defence. In addition to deflection, other ways to remove the defence include capturing the defender, attacking the defender, and interference.
It is also possible to deflect the defender of a square, for example of a square where a checkmate, or a fork is possible. You can learn these combinations in the following levels: