Tactics: Discoveries

Discoveries can be extremely painful to the victim.  The idea behind a discovery is that one of your pieces moves out of the way of the line of attack of another one of your pieces, thus "discovering" a new threat.  The piece that is moving to allow the attack can often make what would normally be insane or suicidal moves.

This is a discovered check.  When black moves the bishop, his rook puts white's king in check.  At the same time, black's bishop is attacking white's queen.

White wins black's queen with this discovery.  The checking bishop forces black to respond, and he cannot save his queen.

Any good opponent should see a discovery coming, but even if he does, you can often use the threat of a discovery to force him to make a move he might not have spent time on.  Generally, it is best to set up a discovery by moving the blocking piece into place first, and then the "discovered attacker" in afterwards.  Another opportunity to set up a discovery is when you know an exchange of pieces is going to be taking place.

As with other tactics, just because a discovery can be dangerous doesn't mean it always is.  If you see one coming against you, don't immediately panic.  Make sure there is actually some poison in the move before deciding you have to react to it.