Controlling our emotions — especially the wild, uncontrolled passion of anger — helps everyone. But it helps kings even more than ordinary people. When someone has enough power to act on every angry impulse, everything falls apart. Power can't last long if it's used to hurt many people. Eventually, common fear will unite people who have been suffering alone. Many kings have been killed because of this — some by individuals, others by entire populations who were so outraged they chose one person to carry out their revenge.
This control of our passions, and especially of this mad and unbridled passion of anger, is useful to subjects, but still more useful to kings. All is lost when a man’s position enables him to carry out whatever anger prompts him to do; nor can power long endure if it be exercised to the injury of many, for it becomes endangered as soon as common fear draws together those who bewail themselves separately. Many kings, therefore, have fallen victims, some to single individuals, others to entire peoples, who have been forced by general indignation to make one man the minister of their wrath.