White's open three on row 7 demands an answer — but the best answer hits back. Black's column 9 stands at (9,4), (9,5), (9,6): one stone from a rush four, and the missing stone is (9,7) — the open three's right end. Find the point that blocks the three AND completes the four at the same time: 防守反击, the counter inside the defense. When such a square exists, plain defense is a wasted opportunity.
Finish this step to move on.