The Use of Spies - Aim of spying in all its five varieties is used for the knowledge of the enemy.

“If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle.” ― Sun Tzu, The Art of War

Sun Tzu wrote this classic book twenty-five hundred years ago, on a military strategy based on Chinese warfare and military thought. It is composed of 13 chapters. Each one is devoted to an aspect of warfare and how it applies to military strategy and tactics. Since that time, these teachings have adapted for use in politics, business, and everyday life and stands immensely relatable in our contemporary world.