I'm placing my piece in column 5, which will land at position (3,5). This creates a horizontal threat with my existing O at position (3,4). If I can later play at position (3,6), I would have a horizontal win. This move doesn't give my opponent any immediate winning opportunities, and it sets me up for potential future winning lines. Even if my opponent blocks my horizontal threat by playing at column 6, I'll still have other strategic options available.