"When you are ignorant of the enemy but know yourself, your chances of winning or losing are equal."

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War is the realm of uncertainty; three-quarters of the factors on which action in war is based are wrapped in a fog of greater or lesser uncertainty. ... war is the realm of chance. No other human activity gives it greater scope; no other has such incessant and varied dealings with this intruder. Chance makes everything more uncertain and interferes with the whole course of events.

— Carl von Clausewitz