假痴不癫　(jiǎ chī bù diān)

Feign Inaction Before an All-out Offensive

Feigning idiocy while keeping tabs on everything happening around you, or feigning inaction while secretly getting yourself ready for action is what this stratagem is all about.

The purpose, of course, is to confuse the enemy about your intentions and motivation, luring them into underestimating you and dropping their guard. Meanwhile, you spare no effort to get ready for a decisive offensive and quietly wait for the right moment.

Sima Yi, one of the best-known strategists in Chinese history, adroitly applied this stratagem in a successful coup detat more than 1,700 years ago.

During the Three Kingdoms Period (220-280 AD), after the young prince of the Kingdom of Wei was enthroned in 239 AD, the imperial court was actually controlled by two top officials, namely, Sima Yi and Cao Shuang.

In the power struggle between the two, Cao first managed to deprive Sima of his military power.(https://www.daowen.com)

Sima then immediately asked for extended sick leave from the imperial court and returned to his hometown with his two sons.

After considerable time, Cao decided to send an envoy to Sima’s home to find out what he’d been doing.

Upon hearing of this, Sima went to bed and pretended to be seriously ill. So, when Cao’s henchman came, he saw a disheveled, senile old man lying in bed, sniveling and babbling all kinds of insane words.

He tried to talk to Sima, but the old man could hardly understand him. So, he returned to the imperial court and told Cao that Sima was ready to die.

Cao was so relieved that he began to fully indulge himself in sensual pleasures and gradually forgot that he still had a potential enemy.

Meanwhile, Sima and his sons sent people to monitor Cao day and night as part of their planning for a comeback.

It was not until 10 years later that Sima and his sons had an opportunity to storm back into the imperial court and seize military power. They did so while Cao was accompanying the young king hunting outside the capital.

A word of advice is that one should never overact as senile or lunatic or behave like an idiot or madman when following this stratagem. Otherwise your enemy will become suspicious and your strategy might fail.