《荀子·劝学》
物性过硬则反易折断，太柔弱了又易被束缚，与人不善会惹来怨恨，干柴易燃，低洼易湿，草木丛生，野兽成群，万物皆以类聚。
草木畴生，禽兽群焉，物各从其类也。
If the material is too hard, it is easy to break, and if it is too soft, it is easy to be restrained. Being unkind to others will attract resentment. Dry firewood is easy to burn, and low-lying areas are easy to get wet. Weeds grow densely and there are many beasts. Everything gathers together.