Authority: Now, the reason a brilliant sovereign and a wise general conquer the enemy whenever they move, and their achievements surpass those of ordinary men, is their foreknowledge of the enemy situation. This “foreknowledge” cannot be elicited from spirits, nor from gods, nor by analogy with past events, nor by astrologic calculations. It must be obtained from men who know the enemy situation—from spies. (Sun-tzu, The Art of War, fourth century B.C.)
