瞒天过海
Stratagems of Winning · 胜战计Deceive the opponent by creating an illusion of normalcy. When something is done repeatedly, it becomes familiar and raises no suspicion.
Emperor Taizong of Tang refused to cross the sea to campaign against Goguryeo due to fear. General Xue Renguo secretly built a magnificent hall on a ship and invited the Emperor to a feast in what appeared to be a grand mansion. The Emperor enjoyed the feast, and only when he heard the waves did he realize he was already at sea — too late to turn back.
While publicly maintaining its image as a computer company, Apple secretly developed the iPhone under "Project Purple." Regular iPod and MacBook updates created business-as-usual that masked the revolutionary work. Competitors Nokia and BlackBerry had virtually no advance warning.
The Allies created an entire phantom army group (FUSAG) under General Patton to convince Germany the invasion would target Pas-de-Calais. Inflatable tanks, fake radio traffic, and double agents maintained the illusion. The real invasion at Normandy achieved near-complete surprise.