He is most powerful who has power over himself.

Seneca the Younger (c. 4 BC-AD 65) Roman statesman, philosopher, playwright [Lucius Annaeus Seneca]

Moral Letters to Lucilius [Epistulae morales ad Lucilium], letter 90, sec. 34 “On the Part Played by Philosophy in the Progress of Man” [tr. Gummere (1918)]