Critically analyze [the enemy] to know the estimations for gain and loss. Stimulate them to know the patterns of their movement and stopping. Determine their disposition of force (hsing) to know the tenable and fatal terrain. Probe them to know where they have an excess, where an insufficiency. Thus the pinnacle of military deployment approaches the formless. If it is formless, then even the deepest spy cannot discern it or the wise make plans against it.
Sun Tzu, The Art of War, c. 450 BCE