I was pointing at a thundercloud and saying that lightning may strike, and my Chinese friend said a 4-syllable phrase that meant that it happened just as I finished talking about it.
Do you know this phrase?
一语成谶 (yī yǔ chéng chèn)
It is not easy guessing what that phrase is without knowing whether it is Mandarin or Cantonese. In Cantonese it could be the colloquial 一講曹操 referring to 一講曹操，曹操就到. Its English equivalence is speak of the devil.
(I'm not sure if in Mainland/Taiwan Mandarin whether people just use the first half as 方說曹操 or 一講曹操 etc.)