《孙子兵法·军形篇》
做到不会被敌人战胜的关键，在于自己创造充分的条件；战胜敌人则关键在于敌人出现可乘之隙。所以，善于指挥作战的人，先要做到不会被敌人所战胜，然后待机战胜敌人。
不可胜在己，可胜在敌。故善战者，能为不可胜，不能使敌之必可胜。
The key to being invincible lies in the creation of favorable conditions; the key to defeating the enemy lies in catching the enemy off guard. Therefore, a skillful commander, first ensures he himself will not be defeated by the enemy, and then waits for the right moment to defeat the enemy.