ㄖㄨㄛˋruòㄧㄠˋyàoㄖㄣˊrénㄅㄨˋzhīㄔㄨˊㄈㄟchúfēiㄐㄧˇㄇㄛˋㄨㄟˊwéi

若要人不知,除非己莫为
  1. 人家知道除非自己未曾只要壞事一定知道無法永遠隱瞞 若要人不知,除非己莫為當年惡行今天公諸於世」。

If you don't want anyone to know, don't do it (idiom)​. fig. If you do something bad, people will inevitably hear about it.