Bluffing is usually thought of in playing poker, not chess, but it does apply to the
game of chess even though it is unsuccessfully applied at times. Many opponents
will attempt to bluff by placing pieces in an open space on their side of the
board with no real objective to sacrificing the piece.

At the beginning of the game to many people who play chess, this happens when your opponent is trying
to get a feel for you. An opponent may run a bishop or knight out to your side of the board in the beginning simply as an attempt to establish an offensive front.

The player who ignores this piece and allows it to sit there on the board while carrying
out their own plan gives your opponent an advantage. You must find out if your opponent is bluffing
and trying to feel you out. In a chess game, if you challenge this piece, your opponent may very well retreat instead of standing to fight.

As in a game of poker, your opponent wants to see what type of player you are. They are trying to see if you are an aggressor or a protector of your pieces. When you call the bluff from your opponent, it enables you to find out how badly they want to keep this piece in the middle of the board.

If you do nothing and just allow this piece to sit, before you as an aggressor, then you are giving your opponent the advantage. In a worst-case scenario you will simply trade a bishop for a bishop, or a knight for a knight.

This is still a great protective move made by you. For the simple reason that leaving
the piece sitting out there unchallenged as the game goes on will prove to be a
thorn in your side. Always Challenge every piece that comes onto your side of
the board in chess and then determine how strongly your opponent feels about
keeping that piece there, or if they will simply cower and retreat.