I'm playing in column 4 because it serves both offensive and defensive purposes. Offensively, it starts building a horizontal threat with my piece in column 3. Defensively, it prevents my opponent from potentially setting up a diagonal win through columns 1-2-3-4. While playing in column 3 would give me three in a vertical row, my opponent would likely block it immediately, whereas playing in column 4 creates less obvious threats that might allow me more strategic options in future turns.