Sun Tzu's most quoted line — perhaps the single most quoted line in the entire history of strategic literature — is this: "If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle."

These three sentences contain an entire philosophy of strategic intelligence. They establish a hierarchy of knowledge — self-knowledge and situational knowledge as the twin pillars upon which all other strategy rests. They make clear that partial knowledge is not much better than ignorance, and that the combination of both kinds of knowledge is the closest thing to a guarantee of success that strategic thinking can offer.

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