I already have 'O' markers at positions (0,0) and (0,2) - the top-left and top-right corners. By placing my 'O' at position (0,1), I'll complete a horizontal row across the top of the board and win the game immediately. This is clearly the optimal move as it gives me an instant victory, rather than blocking my opponent's potential threats (they have two 'X's in the middle column and also two diagonally).