《战国策·赵三·赵惠文王三十年》
况且那吴国的干将之剑虽然锋利，更难得的是如果剑背不足够厚，剑尖就无法刺人；剑面不足够轻薄，剑刃就无法断物。
且夫吴干之剑材，难夫毋脊之厚，而锋不入；无脾之薄，而刃不断。
Moreover, although the sword of Ganjiang of Wu is sharp, it is more difficult to note that if the back of the sword is not thick enough, the tip of the sword cannot pierce people; if the face of the sword is not thin enough, the blade of the sword cannot cut things.