This chapter introduces the term shih, one of the key terms of the Art of War. Most simply said, shih is the ever-changing configuration of power in one's environment. The skilled general knows shih so well that he/she can use it to achieve effortless victories. For example,

One who uses shih sets people to battle as if rolling trees and rocks.
As for the nature of trees and rocks --
When still, they are at rest.
When agitated, they move.
When square, they stop.
When round, they go.

Thus the shih of one skilled at setting people to battle is like rolling round rocks from a mountain one thousand jen high.

Chapter 5 also contains the famous pair "orthodox and extraordinary." The former is battle-by-the-book, what the enemy expects. The latter is always unpredictable. Thus:

In sum, when in battle,
Use the orthodox to engage.
Use the extraordinary to attain victory.