The essential factor of military success is speed, that is taking advantage of others' unpreparedness or lack of foresight, their failure to catch up, going by routes they do not expect, attacking where they are not on guard. This you cannot accomplish with hesitation.
War is a matter of vital importance to the state; the province of life or death; the road to survival or ruin. It is mandatory that it be thoroughly studied.
So a military force has no constant formation, water has no constant shape: the ability to gain victory by changing and adapting according to the opponent is called genius.
It is only the enlightened ruler and the wise general who will use the highest intelligence of the army for the purposes of spying, and thereby they achieve great results.