I'm playing in column 0 because it gives me an immediate horizontal win. I already have three O pieces in positions (5,1), (5,3), and (5,4) in the bottom row. By placing my piece in column 0, I'll create a line of 4 O's horizontally and win the game. There's also a defensive reason to play - my opponent has three X pieces in column 4 and could win vertically on their next turn, but my winning move takes precedence.