The fear of the tyrants.

What the tyrant fears—Internal fear: The tyrant is constantly tormented by fear, suspicion, and inner turmoil because his reason and soul are dominated by lawless desires. Fear of his subjects: Because he oppresses everyone and can trust no one, the tyrant lives in constant fear that his citizens will depose or assassinate him. The necessity of war: Plato describes how, once a tyrant has dealt with foreign enemies, he must constantly instigate new wars so that the people remain in need of a leader and fearful of the outside world. The paradox of power—The true slave: Although a tyrant seemingly possesses absolute power, in reality, he is the greatest slave of all. He must act in a flattering and servile manner toward the worst kind of people to maintain his power. The misery of the soul: According to Plato, the tyrannical soul is its own worst enemy, characterized by a perpetual state of panic and a lack of freedom.

Plato : The Republic