I'm playing in column 4 for both defensive and offensive reasons. Defensively, I'm preventing my opponent from creating a horizontal three-in-a-row threat in the middle of the board (they already have X pieces at columns 2 and 3 in row 3). Offensively, this move creates a vertical pair with my existing O piece at the bottom of column 4, giving me the potential to build upward for a vertical win. This central position also maintains flexibility for future diagonal or horizontal connections.