In order to cause the enemy to come of their own volition, extend some apparent profit. In order to prevent the enemy from coming forth, show them the potential harm. ... When someone excels in attacking the enemy does not know where to mount his defense; when someone excels at defense, the enemy does not know where to attack. Subtle! Subtle! It approaches the formless. Spiritual! Spiritual! It attains the soundless. Thus he can be the enemy's Master of Fate.
Sun Tzu, The Art of War, c. 450 BCE