《孙子兵法·九地篇》
深入敌国作战的规律是：进入敌境越深，士卒就越专心一致，进入得浅，士卒就容易逃散。
凡为客之道：深则专，浅则散。
<6>. The law of fighting deep into a enemy country is: the deeper the soldiers enter the enemy territory, the more unanimous they will be; the more shallowly they enter, the easier it will be for the soldiers to escape.