1.E6 eventually forces Black to relinquish a "won" quadrant game.

In themselves, the quadrant games are tied 2-2: White has the right game and the upper game, and Black has the left game and the lower game. Observe that the stone White places at E6 is guaranteed to reach the lower right side of the large game. Therefore, Black must play 2.F7 to prevent it from reaching the upper left side of the large game and winning it. White plays 3.E7 and Black must again defend the large game with 4.F9.

Now White plays 5.B8! and steals the left quadrant game from Black, who probably thought for sure he had it. But by threatening the large game with 1.E6 and 3.E7, White essentially gained two "free" moves in that quadrant, enabling the play at B8 to work. The sequence 6.D9 7.C7 8.D8 9.C6 ensues --- Black can still win the large game but loses three quadrants for an overall 2-3 defeat.