自知之明
齐国大夫长得很漂亮。 一天早晨，他照着镜子，问妻子说：“我和徐公比，谁漂亮？” 妻子回答说：“你漂亮，徐公怎能跟你比呢！“ 徐公是齐国美男子，大夫对妻子的回答不大相信，他又问他的妾：”我和徐公比，谁漂亮？“ 妾也说：“徐公怎能跟你比！”
第二天，来了一位客人，大夫和他聊天儿，就问他： “我和徐公谁漂亮？” 客人说：“徐公不如你漂亮！” 又过了一天，徐公来看大夫。 大夫感到自己不如徐公漂亮。大夫想：我不如徐公漂亮，可是妻子，妾，客人都说我比徐公漂亮，这原来是因为：妻子爱我，妾怕我，客人要我帮忙。
他把这个想法告诉齐王，提醒他不要轻易相信别人的好话。齐王觉得十分有道理。
成语 Chéngyǔ，similar to English idiom, is a word group or a phrase which is established through usage and practice. Unlike English idiom, a Chéngyǔ is often made of a fixed number of Chinese characters, and most Chéngyǔ (98%) have four characters. Chéngyǔ often contain literary allusions which were derived from analogy or historical stories. The meaning of a Chéngyǔ is often much more difficult to derive from its constituents than an average English idiom. While some modern Chéngyǔ have a direct literal translation in other languages, many Chéngyǔ do not have a foreign language equivalent due to their strong historical background. One, who is able to master the use of Chéngyǔ, is considered as well-educated and receives respect.