A thorough knowledge of both oneself and the enemy will avoid peril even in a hundred battles. This principle of warfare was proposed by the ancient military thinker Sun Wu. He advised that the commanding officer must first investigate and scout out the adversary thoroughly so as to know the strengths and weaknesses of both sides. This will give him foresight in battle and prevent reckless actions. Such knowledge is key to correct leadership, maintaining the initiative, and overcoming the adversary. This general principle applies to all other kinds of conflicts, too.

Know yourself as well as your enemy and you will know no peril even in a hundred battles. Know yourself but not your enemy and you will only win half your battles. Knowing neither yourself nor your enemy means peril in every battle. (The Art of War)