Chapter 1, Verse 26 - Sun Tzu

Now the general who wins a battle makes many calculations in his temple ere the battle is fought. The general who loses a battle makes but few calculations beforehand. Thus do many calculations lead to victory, and few calculations to defeat: how much more no calculation at all! It is by attention to this point that I can foresee who is likely to win or lose.
~ from The Art of War, Giles translation ~

Go here to read the introductory post to the verses of The Art of War.