The Chinese idiom 守口如瓶 (shou3 kou3 ru2 ping2) literally means keep your mouth shut as tight as a jar lid. It comes from a story about a talented young man, Fu Bi, who lived during the Northern Song Dynasty.
Fu's talent and learning was recognized by the famous Chinese scholar Fan Zhongyan. While Fu was still relatively young, Fan recommended him to the minister in charge of military affairs in the imperial court. From here, Fu went from strength to strength and he rose rapidly from the ranks to become prime minister of the imperial court.
However, Fu did not see eye to eye with his colleague Wang Anshi, a well known reformer of the time. Fu was worried about what would happen should Wang ever become prime minister of the court.
One day the emperor asked Fu to recommend someone as his successor. Fu suggested a number of officials, but not Wang. The emperor was a little surprised. He asked Fu whether he thought Wang was a worthy candidate. This time Fu remained tight lipped, and it suddenly dawned upon the emperor that Wang and Fu did not get along. The emperor later came to support Wang's bold rural economic reform program, so Fu resigned and move back home.
When later asked by friends about his most important rule for success in political life, Fu related this story about Wang to illustrate that:
You must keep your mouth shut as tight as a jar lid.
Today, Chinese people use the idiom 守口如瓶 (shou3 kou3 ru2 ping2) to describe people who are able to keep things confidential.