一期一会 (いちごいちえ): once-in-a-lifetime encounter; uniquely precious experience; one lifetime, one meeting

once-in-a-lifetime encounter; uniquely precious experience; one lifetime, one meeting

From the tea ceremony: this meeting will never recur, so treat it as unrepeatable. The most quoted yojijukugo in Japan.

A Japanese proverb (ことわざ)