This idiom has a fascinating origin story that has flipped in meaning over time. It comes from the classic text Mencius (《孟子》). The original phrase was “出乎尔者，反乎尔者也” (chū hū ěr zhě, fǎn hū ěr zhě yě), which meant, “Whatever comes from you will return to you.” It was a lesson about karma—if you treat others well, you will be treated well in return. However, the modern usage of 出尔反尔 has lost this original meaning. Today, it describes how a person's words “go out” (出) from “you” (尔), but are later “reversed” or “returned against” (反) by “you” (尔) yourself. It now signifies self-contradiction and breaking a promise.
In Chinese culture, trustworthiness and keeping one's word (守信, shǒuxìn) are paramount virtues. A person's word is seen as a reflection of their honor and character. To 出尔反尔 is to commit a serious social foul, causing one to lose “face” (面子, miànzi) and be deemed unreliable. A useful Western comparison is the phrase “to change one's mind.” While they can overlap, their cultural weight is very different.
Accusing someone of 出尔反尔 is a direct challenge to their integrity (信用, xìnyòng). It’s not a light-hearted comment; it's a way of saying, “Your words mean nothing, and I can no longer trust you.”
This idiom is common in situations where a commitment has been broken.
The connotation is always negative and accusatory. It is a formal idiom but is used in both formal writing and heated informal conversations.