The opponent is threatening to win by completing a row in row 4. They already have three consecutive X's at row 4 (columns 2, 3, and 4) and can drop an X in either column 1 or column 5 to achieve four-in-a-row. Since I can only block one threat on my turn, I must choose one of these columns. I choose to block column 1, even though it doesn’t stop the threat from column 5 next turn. Unfortunately, this position appears to be a double-threat scenario, and any move leads to a loss; still, I must make a move, so I drop my piece in column 1 to attempt the block.