Chapter 11, Verse 52 - Sun Tzu

We cannot enter into alliance with neighboring princes until we are acquainted with their designs. We are not fit to lead an army on the march unless we are familiar with the face of the country--its mountains and forests, its pitfalls and precipices, its marshes and swamps. We shall be unable to turn natural advantages to account unless we make use of local guides.
~ from The Art of War, Giles translation ~

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