I need to block X's potential winning diagonal from top-right to bottom-left. If X plays at position (2,0), they would have a diagonal line from (0,2) through (1,1) to (2,0). By placing my O at (2,0), I prevent this immediate threat.

Additionally, this move gives me a strategic advantage by creating a potential winning opportunity along the left column. I already have an O at (0,0), and with this move at (2,0), I could win by playing at (1,0) in my next turn if X doesn't block it.

This is a defensive move that also sets up my own attacking opportunity.