From the "Attack by Stratagem" chapter of The Art of War by Sun Tzu:
17. . . . There are five essentials for victory:
- He will win who know when to fight and when not to fight.
- He will win who knows how to handle both superior and inferior forces.
- He will win whose army is animated by the same spirit throughout all its ranks.
- He will win who, prepared himself, waits to take the enemy unprepared.
- He will win who has military capacity and is not interfered with by the sovereign.
Victory lies in the knowledge of these five points.
18. Hence the saying: 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.