Controlling the center is a key idea in chess, but a rather difficult to understand one. Seizing the center means being able to put pieces there uncontested. Moreover, when pieces are in the center, they can access the most squares. It logically follows that the greatest threats are from the center, thus an attack on the wing is trumped by one from the middle of the board.
In the following game, black erred by choosing the wrong way to achieve counterplay; black's plan of queenside expansion and material gain was trumped by white's direct attack on the center.
In this position, black has a choice:
- Lock pawns by pushing ...c4, then controlling the queenside by bringing in the knight to b5.
- Break on d4, and occupy the open file with rooks, and post a knight or rook on c4.
White, on the other hand, has a straightforward plan. Having the central pawn majority, white's goal is to advance them to the end, with support from all his pieces. (For the record, note that white's bishop is misplaced due to an opening blunder. Forgive the players for such opening inaccuracies because the Nimzo-Indian was still much unexplored at the time!)
By this time, black has succeeded in his goal. He has won a pawn on the wing, and the knight is situated in a powerful outpost. Black's follow-up seems fine and dandy--advance the queenside majority until a pawn hits the end... right? The pleasant position for black is deceiving.
What white has going is a central attack which will ultimately prevail, simply because it is faster. It can be supported by pieces from all directions, while black's attack on the wing requires more time to achieve.
A key idea in many variations is that the black queen is stranded in the corner. Remember that thing about pieces in the center being powerful because they're more mobile? The positions and variations leading up to move 27 demonstrate that pieces on the edge of the board are much less useful than ones that have more access to the center: black's queen and knight are practically useless in defending against white's central attack with a queen and knight.
This game demonstrates the importance of considering both sides' plans when choosing a plan yourself. By locking up the center, black gave white the advantage of a kingside attack with a head start, since white's pawns already controlled the center uncontested.
To wrap up, I'd like to go briefly touch on how black should have done at the turning point: