Chapter 4, Verses 17 and 18 - Sun Tzu

In respect of military method, we have, firstly, Measurement; secondly, Estimation of quantity; thirdly, Calculation; fourthly, Balancing of chances; fifthly, Victory. Measurement owes its existence to Earth; Estimation of quantity to Measurement; Calculation to Estimation of quantity; Balancing of chances to Calculation; and Victory to Balancing of chances.
~ from The Art of War, Giles translation ~

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