I need to block my opponent from winning. If I don't place my O at position 1,2, my opponent could place an X there to complete three Xs in the middle row (1,0 - 1,1 - 1,2). This is an immediate threat I must block.

While I can't create a winning line for myself with either of the available moves, blocking the opponent's winning opportunity is the priority. After I place my O at 1,2, the board will have only one empty space at 2,0, which means the game is likely to end in a draw with optimal play.