I'm playing in column 0 because it extends my existing pieces at (1,5) and (2,5) into a horizontal three-in-a-row. This starts creating my own threat while developing the left side of the board. While my opponent has three vertical pieces in column 3, they won't be able to win on their next move since they still need multiple moves to complete that vertical line. By building my horizontal threat, I'm creating offensive pressure rather than just playing defensively.