People who take ample precautions are liable to be off guard. Familiar sights do not rouse suspicion. Yin is the inner instead of the opposite aspect of yang. The great yang contains the great yin.

This expression came from the story of an ingenious Tang general who devised a method to transport the emperor (regarded as the son of heaven in imperial China) safely across the sea, without the emperor’s own knowledge. The word heaven may also be interpreted literally. In ancient times it was easy to initiate military wars on land because mountains and forests can be perfect natural shelters, while the sea has not hiding areas. Therefore, in order to cross the sea, one has to move over the sea but act as he/she did not want to.