善人者不善人之师，不善人者善人之资。不贵其师，不要其资，虽智大迷。是谓要妙。
《老子》第27章
The good man is the teacher of the bad, and the bad man is the material from which the good man learns, He who does not honor his teacher and who does greatly care for the material is greatly confused though he thinks himself wise, Such is the subtle essence,
[注释]
资:资助、凭藉的意思。孔子说:“三人行，必有我师焉。择其普者而从之，其不善者而改之。”(《论语，述而》)也是这个意思。贵师、爱资;普者为师，恶者为资，这是事物所包涵的对立的两个方面。要妙:即微妙要道。“这里指善人为不善人之师，不善人为善人之资，善与不善互为转化，这就叫做微妙的要道。
[译文]
善人是不善人的老师，不善人是善人的鉴戒。如果不尊重老师，不爱惜鉴戒，即使是智慧者也会大迷不悟。这就是为人处事微妙的要道。