All warfare is based on deception. Hence, when able to attack, we must seem unable; when using our forces we must seem inactive; when we are near, we must make the enemy believe that we are away; when far away, we must make him believe we are near. Hold out baits to entice the enemy. Feign disorder and crush him.
—Sun Tzu, 544 BC – 496 BC
If you don’t use this advice yourself, at least be cognizant of when it is being used against you.