Black’s knight on b4 and bishop on f5 menacingly eye white’s c2 square. The bishop is poised to support the knight’s invasion of c2, forking black’s king and rook. How should white respond to this threat?

In chess notation, the board is a grid: the vertical columns are numbered “1” through “8;” the horizontal rows, “a” through “h.” Each square on the board is identified by a specific letter and number. For example, if the white knight at f3 were to move to e5, the notation would be ne5 (n=knight, r=rook, b=bishop, q=queen, x=take, +=check, etc.) . . . First, white cannot counter black’s threat with an equal or greater threat. White must, therefore, stop black’s threat.

The most direct response is bd3. Black then captures the bishop with the b4 knight. Since white cannot recapture with the queen, white’s c2 pawn takes the knight.

White’s isolated, doubled pawns are a lasting weakness. Equally important is the loss of the light-squared bishop. Black can now dominate the light-squares with its own light-square bishop.

White’s best response is to move its bishop from f1 to b5, checking black. If black blocks the check with its b8 knight or its c7 pawn (best), white retreats the bishop to a4.

From a4, the bishop prevents an invasion of c2. Bb5+ also saves the light-squared bishop.

If black blocks the check from b5 with its f5 bishop, white simply castles and has a superior position. Blocking the check with the f5 bishop effectively gives white an extra move.

The game is even after bb5+ with many more moves ahead. Eventually one player will make a mistake comparable to bd3. The lesson here is that a bad move is always as close as one move away.