不期而遇

Origin and story

Guliang Zhuan (穀梁傳), Duke Yin’s eighth year, comments on the rulers of Song and Wei meeting at Chui. It explains the historical term 遇 as a meeting without an appointed arrangement, using the wording 不期而会. A related discussion in Gongyang Zhuan likewise distinguishes this sort of encounter from a formally arranged meeting.

The idiom later takes 遇 into the phrase itself. It describes an encounter that neither party planned, not necessarily one between strangers and not necessarily a happy coincidence. The diplomatic classification in the old commentary has become an ordinary way to speak about running into someone unexpectedly.