《淮南子·兵略训》
所以，用兵贵在于谋略不被测度，部队行动隐藏不露，常常能出其不意使对手无法设防。
兵贵谋之不测也，形之隐匿也，出于不意、不可以设备也。
Therefore, the key to military strategy lies in devising plans that cannot be fathomed and keeping troop movements hidden, so as to often catch the enemy off guard and prevent them from defending themselves.