Marcus Aurelius, from Exhortations to Himself
Remember that your reason is invincible when you are in control — that is, doing nothing you choose not to do — even if your resistance is only the choice to be obstinate.
The mind free from uncontrolled emotion is a citadel; it is an impregnable sanctuary and we have no more secure place to run to. Those who have not realized this are ignorant, and those who have realized it but do not use their insight are unhappy. VIII, 48