《孙子兵法·九变篇》
所以将帅精通 九变 的具体运用，就算是真正懂得用兵了；将帅不精通 九变 的具体运用，就算熟悉地形，也不能发挥其有利作用。将帅指挥作战如果不懂 九变 的方法，即使知道五种地形的利与弊，也不能充分发挥部队的战斗力。
故将通于九变之利者，知用兵矣；将不通九变之利，虽知地形，不能得地之利矣；治兵不知九变之术，虽知五利，不能得而用之矣。
Therefore, if a marshal is proficient at using the specific applications of the nine changes, they truly understand how to use troops; if a marshal is not proficient at employing the specific applications of the nine changes, they cannot utilize the favorable advantages, even if they are acquainted with topography. If a marshal commands warfare without understanding the methods of the nine changes, then even if they know the advantages and disadvantages of the five land types, they cannot fully bring out the combat power of the troops.