"Pay respect to the elders and take the suggestions of the intellectuals; treat them as your teachers.
Consider those who will not flatter but always criticize you. Because good and bad, kind and evil, and right and wrong are not easy to tell apart.
Some things are similar in appearance but different in nature. For example, green bristle grass seeds can look like rice. The hide of the cow is the same color as the tiger's. Bone can be mistaken for ivory and worthless stone for pure jade.
All of these are apparently right, but actually wrong. So if you want to distinguish between them, you must observe them carefully."
- Duke Wei-Wen
Tang Dynasty Official