Chapter 6, Verse 16 - Sun Tzu

The spot where we intend to fight must not be made known; for then the enemy will have to prepare against a possible attack at several different points; and his forces being thus distributed in many directions, the numbers we shall have to face at any given point will be proportionately few.
~ from The Art of War, Giles translation ~

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