Sun Tzu, answered from the texts and cited to the page.
The art of war is of vital importance to the State.1 That is the whole answer, and everything else follows from it. War is a matter of life and death, a road either to safety or to ruin — and because it is that, it is a subject of inquiry which can on no account be neglected.2 A ruler who does not understand the conditions of war, a general who does not know the five constant factors, will fail; and when a general fails, it is not he alone who pays.3
The army pays. The state pays. So I set down what can be known, what can be compared, what can be calculated before the first soldier moves. The seven comparisons — which sovereign holds the Moral Law, which general has the greater ability, where Heaven and Earth give advantage, where discipline is enforced, where the army is stronger, where training runs deeper, where reward and punishment are constant — these are the means by which victory or defeat can be forecast.4
I wrote so that a ruler or commander who hearkens to this counsel and acts upon it will conquer, and one who does not will suffer defeat.5 That is why the thirteen chapters exist: not for glory, not for theory, but because the province of life and death demands that someone look at it clearly and set down what they see.
The art of war is of vital importance to the State.The Art of War
It is a matter of life and death, a road either to safety or to ruin. Hence it is a subject of inquiry which can on no account be neglected.The Art of War
These five heads should be familiar to every general: he who knows them will be victorious; he who knows them not will fail.The Art of War
By means of these seven considerations I can forecast victory or defeat.The Art of War
The general that hearkens to my counsel and acts upon it, will conquer:—let such a one be retained in command! The general that hearkens not to my counsel nor acts upon it, will suffer defeat:—let such a one be dismissed!The Art of War