Book XI · 7
How plain does it appear that there is not another condition of life so well suited for philosophizing as this in which thou now happenest to be.
How clearly is it borne in on thee that there is no other state of life so fitted to call for the exercise of Philosophy as this in which thou now findest thyself.
Marcus Aurelius, Meditations XI.7. Translated by George Long (1862). The Stoic Library.