《战国策·赵三·平原君请冯忌》
赵国用七败的余兵，收合了破散的败兵守卫邯郸城，然而秦国的攻城部队却在邯郸城下弄得疲倦不堪，赵国坚守不可攻破的缘故，是因为攻城困难防守容易。
赵以亡败之余众，收破军之敝守，而秦罢于邯郸之下，赵守而不可拔者，以攻难而守者易也。
Zhao used the remaining soldiers of the seven defeats to collect the scattered defeated soldiers to defend Handan. However, the Qin army that attacked the city was exhausted under Handan. The reason why Zhao was unable to attack and defend was because it was difficult to attack and defend.