Deceive the heavens to cross the ocean (瞞天過海)
Prepare too much and you lose sight of the big picture; what you see often you do not doubt. Yin (the art of deception) is in Yang (acting in open). Too much Yang (transparency) hides Yin (true ruses).
This stratagem references an episode in 643 AD, when Tang emperor Tang Gaozong Li Simin, balked from crossing the sea to a campaign against Koguryo. His General Xue Rengui thought of a stratagem to get the Emperor across and allay his fear of seasickness: on a clear day, the Emperor was invited to meet a wise man. They entered through a dark tunnel into a hall where they feasted. After feasting several days, the Emperor heard the sound of waves and realized that he had been lured onto a ship! General Xue drew aside the curtains to reveal the ocean and confessed that they had already crossed the sea: Upon discovering this, the emperor decided to carry on and later completed the successful campaign.
This stratagem means that you can mask your real goals, by using the ruse of a fake goal that everyone takes for granted, until the real goal is achieved. Tactically, this is known as an 'open feint'; in front of everyone, you point west, when your goal is actually in the east. By the time everyone realized it, you have already achieved your goal. Harro von Senger notes in the German-Language "Die List" that to grasp the full meaning, it would be something like "to deceive the holy virgin Mary" in the West.
Usage
This stratagem makes use of the human failing to become unaware of common everyday activities, or events that appear normal. The best secrets are carried out in broad daylight. The best hoax is to repeat it so often that people are convinced that the next move is also a hoax. When this happens, it is the best moment to carry out one's previously hidden true objective.
In the Second World War, Hitler spread misinformation about a planned date for the Invasion of France, but later delayed the date. This was repeated many times, and eventually France and England grew used to the false information, and regarded all Germany planned invasions as hoaxes. Eventually, Germany invaded France with lightning speed, conquering France.
In the Second World War, the Allies' Operation Quicksilver created a phantom army in Kent complete with faked radio chatter which divided German attentions regarding the actual Allied armies and their intended objective of the Normandy landings.
