I need to block my opponent from winning with a vertical line in the middle column. They already have Xs at positions (0,1) and (1,1), and would win on their next move by placing at (2,1). By placing my O at (2,1), I prevent their immediate win. Additionally, this move opens up the possibility for me to potentially create a winning opportunity on the bottom row in my next move if I can place at (2,0) later. Since there's no way for me to create an immediate win with this move, blocking my opponent's winning threat is the priority.