I need to block position (1,0) immediately because my opponent has Os at (0,0) and (2,0). If they place their next O at (1,0), they'll win with a vertical line in the left column. 

Additionally, by placing my X at (1,0), I'm starting to build my own potential winning line - I'll have Xs at (1,0) and (1,1), setting up for a horizontal win if I can later place at (1,2). This gives me an offensive opportunity while addressing the immediate defensive need.