You Have Power Over Your Mind

A recurring theme throughout the Meditations, Marcus Aurelius's private philosophical journal written during the 170s AD. As emperor, he faced plague, war, betrayal, and the death of most of his children - yet the journal consistently returns to this Stoic principle: the mind is the one domain where sovereignty is absolute. His teacher Epictetus, a former slave, had articulated the same idea from the opposite end of the social hierarchy.