塞翁失马焉知非福 – sai4 weng1 shi1 ma3 yan1 zhi1 fei1 fu2

Literal translation – saiweng (persons name) – lose – horse – how – know – not – blessing

This basically can be translated as “a blessing in disguise” or even “a curse in disguise” ie the opposite.

It comes from a story about an old man named “Saiweng”.  He lost his horse and his friends came to comfort him but he was optimistic saying that it could be a good thing.  He turned out to be correct when sometime later the horse returned bringing with it another better horse.  His friends again came to him this time joyful but Saiweng wasn’t so sure this was a good thing.  Turned out his son broke his leg while riding this new horse.  once again his friends came to comfort him over his son’s injury but Saiweng once again didn’t necessarily view it as a bad thing right away.  Rightly so as the broken leg prevented his son from being conscripted into the army and therefore saved his life.

This proverb is generally used to comfort someone if they have fallen sick or had some sort of catastrophe.  It could also theoretically be used in the opposite way for someone who has had something very good happen to them but I highly doubt it is ever used in this sense, as who ever wants to rain on someone’s parade and spoil the moment ?

So although it can be used to warn people that the apparent good fortune may be bad luck waiting to happen, it is more commonly used to try to cheer up someone who is troubled over some misfortune that has befallen them.