"Thus the castle of each feudal chieftain became a school of chivalry, into which any noble youth, whose parents were from poverty unable to educate him to the art of war, was readily received."

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Spies cannot be usefully employed without a certain intuitive sagacity; They cannot be properly managed without benevolence and straightforwardness; Without subtle ingenuity of mind, one cannot make certain of the truth of their reports; Be subtle! be subtle! and use your spies for every kind of warfare; If a secret piece of news is divulged by a spy before the time is ripe, he must be put to death together with the man to whom the secret was told.

— Sun Tzu