Looking at the current board, I see that my opponent (X) has placed marks at the top-right (0,2) and middle (1,1) positions, forming a potential diagonal threat. If I don't block properly, they could win by placing X at the bottom-left (2,0) position.

By placing my O at the bottom-left (2,0), I accomplish two things:
1. I block their potential diagonal win (0,2 → 1,1 → 2,0)
2. I start creating a potential vertical win opportunity for myself in the left column (0,0 → 1,0 → 2,0)

This is a defensive move that also begins setting up my own winning possibilities. After this move, I'll have my symbols at the top-left (0,0) and bottom-left (2,0), which means I could potentially win by placing an O at the middle-left (1,0) position in a future turn.