I need to block my opponent's immediate win threat. They have three X's in a row at positions (2,4), (3,4), and (4,4). If they place a piece in column 5, they would create four in a row and win. By placing my piece in column 5, it will land at position (5,4), blocking their potential win. This defensive move is critical as it prevents an immediate loss, while also potentially setting up future opportunities for me.