This is not merely the general's ability to estimate numbers correctly, as Li Ch`uan and others make out. Chang Yu expounds the saying more satisfactorily: "By applying the art of war, it is possible with a lesser force to defeat a greater, and vice versa. The secret lies in an eye for locality, and in not letting the right moment slip. Thus Wu Tzu says: 'With a superior force, make for easy ground; with an inferior one, make for difficult ground.'