Today it's Stratagem 32:
The Empty Fortress
Those who are empty, empty it. Create uncertainty inside uncertainty. Between hard and soft, be strange and strange again.
Empty or full [weak or strong], there are no constants in warfare. Of weak armies who show openly their weakness, ever since Zhuge Liang, there have been many.
For example when the Tibetans conquered Guazhou [in 776], Wang Junhuan died, and the West edges of the Yellow River all fell into panic. Zhang Shougui, governor of Guazhou, took the remainer population and started to build a new fortress. With the scaffolding for the walls was just finished the enemy attached again.
They had no means of defense, and everyone immediately turned pale, with no will to fight. Wang then gave a speech: "The enemy are many, and we are few. We've just survived a defeat, we can't fight again with arrows and stones, we must use other means to defeat them". Saying this he went to the top of the fortress, served some wine, played some music, and held a banquet with his soldiers. The enemy on seeing this thought the fortress was well prepared, so they retreated.
Or like Zu Ting...