The Prince by Niccolo Machiavelli Chapter 10 Page 5

days, when the first ardour has abated, the injury is already done and suffered, and cannot be undone; and the people will now, all the more readily, make common cause with their Prince from his seeming to be under obligations to them, their houses having been burned and their lands wasted in his defence. For it is the nature of men to incur obligation as much by the benefits they render as by those they receive.

Wherefore, if the whole matter be well considered, it ought not to be difficult for a prudent Prince, both at the outset and afterwards, to maintain the spirits of his subjects during a siege; provided always that victuals and other means of defence do not run short.