By playing in column 4, I'll create a horizontal sequence of three O pieces (in positions (5,2), (5,3), and (5,4)). This creates an immediate threat that forces my opponent to block either in column 1 or column 5 in their next turn. This gives me control of the game tempo while also developing my position. Additionally, playing in column 4 doesn't set up any immediate advantage for my opponent, as the piece above this position doesn't create any obvious winning opportunities for them.