I need to block my opponent's immediate win opportunity - they have Os at (0,0) and (0,2) and could win by completing the top row with a move at (0,1). Additionally, by placing an X at (0,1), I create a potential winning line in the middle column (0,1)-(1,1)-(2,1). This gives me two paths to victory - either completing the middle column by playing at (2,1) later, or developing other strategies from this stronger position. This defensive move has offensive value as well.