The Art of War by Sun Tzu

I Laying plans contd...

18,19 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 we are far away; when far away we must make him believe we are near.

Notes by Zephyrist:

This is a variation of the key to winning a battle is 'the element of surprise'. Distract your enemy from seeing how you intend to attack and you can win because they will be unprepared.

Sun Tzu says that you must deceive the enemy into believing that you would not attack in that way. For the world war 2 d-day preparations the allies went to some lengths to persuade Hitler that they were going to attack across the straits of Dover in order to give the allies the elements of surprise on the beaches they actually attacked. The allies forced Hitler to keep his reserves farther back because he did not know where the allies were going to land which gave the allies more time to secure a beach head.