Playing in column 4 creates a vertical threat with 2 Os in a row. If my opponent doesn't block in their next turn, I could play in column 4 again and have 3 Os vertically, setting up a win on my following move. This forces my opponent to play defensively rather than pursuing their own strategy. Other options like columns 2 or 5 create horizontal pairs but don't establish as strong a threat. Column 4 is the most strategic choice as it begins building a vertical winning opportunity while forcing my opponent to respond to my threat.