I need to block the opponent's potential diagonal win. The opponent has X in positions (1,1) and (2,2), forming a diagonal line. If they place their next X at (0,2), they would win with a diagonal from bottom-left to top-right. By placing my O at (0,2), I prevent this win.

Additionally, this move gives me a potential winning opportunity along the top row, as I already have O at (0,0). If I can later place an O at (0,1), I would create a horizontal win across the top row.

This is a defensive move that also sets up a future winning opportunity.