Chapter 11, Verses 50 and 51 - Sun Tzu

On hemmed-in ground, I would block any way of retreat. On desperate ground, I would proclaim to my soldiers the hopelessness of saving their lives. For it is the soldier's disposition to offer an obstinate resistance when surrounded, to fight hard when he cannot help himself, and to obey promptly when he has fallen into danger.
~ from The Art of War, Giles translation ~

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