A prudent captain will do what he can to make it necessary for his own soldiers to fight, and to relieve his enemy from that necessity.
Elsewhere I have noted how greatly men are governed in what they do by necessity, and how much of their renown is due to her guidance, so that it has even been said by some philosophers, that the hands and tongues of men, the two noblest instruments of their fame, would never have worked to perfection, nor have brought their labours to that pitch of excellence we see them to have reached, had they not been impelled by this cause.
The captains of antiquity, therefore, knowing the virtues of this necessity, and seeing the steadfast courage which it gave their soldiers in battle, spared no effort to bring their armies under its influence, while using all their address to loosen its hold upon their enemies.
For which reason, they would often leave open to an adversary some way which they might have closed, and close against their own men some way they might have left open.
Whosoever, therefore, would have a city defend itself stubbornly, or an army fight resolutely in the field, must before all things endeavour to impress the minds of those whom he commands with the belief that no other course is open to them. In like manner a prudent captain who undertakes the attack of a city, will measure the ease or difficulty of his enterprise, by knowing and considering the nature of the necessity which compels the inhabitants to defend it; and where he finds that necessity to be strong, he may infer that his task will be difficult, but if otherwise, that it will be easy.