In antiquity, those that excelled in warfare first made themselves unconquerable in order to await the moment when the enemy could be conquered.
Being unconquerable lies with yourself, being conquerable lies with the enemy.
Thus one who excels in warfare is able to make himself unconquerable, but cannot necessarily cause the enemy to be conquerable.
Thus it is said a strategy for conquering the enemy can be known but yet not possible to implement.
One who cannot be victorious assumes a defensive posture, one who can be victorious attacks. In these circumstances, by assuming a defensive posture, strength will be more than adequate, whereas in offensive actions it would be inadequate.
Those who excel at defence bury themselves away below the lowest depths of Earth. Those who excel at offence move from above the greatest heights of Heaven. Thus they are able to preserve themselves and attain complete victory.
Perceiving a victory that does not surpass what the masses could know is not the pinnacle of excellence. Wrestling victories for which all under Heaven proclaim your excellence is not the pinnacle of excellence.
Those that the ancients referred to as excelling at warfare conquered those who were easy to conquer. Their victories were not marked by fame for wisdom or courageous achievement but were free from errors. One who is free from errors directs his measures toward certain victory, conquering those who are already defeated.
Thus one who excels at warfare first establishes himself in a position where he cannot be defeated while not losing any opportunity to defeat the enemy.
For this reason, the victorious army first realises the conditions for victory, and then seeks to engage in battle. The vanquished army fights first and then seeks victory.
One who excels at employing the military cultivates the Tao and preserves the laws; therefore, he is able to be the regulator of victory and defeat.
As for military methods: the first is termed measurements; the second, estimation of forces; the third, calculation of numbers of men; the fourth, weighing relative strength; and the fifth, victory.
Terrain gives birth to measurement; measurement produces the estimation of forces. Estimation of forces gives rise to calculating the numbers of men. Calculating the numbers of men gives rise to weighing strength. Weighing strength gives birth to victory.
Thus the victorious army is like a ton compared with an ounce, while the defeated army is like an ounce weighed against a ton! The combat of the victorious is like the sudden release of a pent-up torrent down a thousand-fathom gorge. This is the strategic disposition of force.