Book XI · 29
Neither in writing nor in reading wilt thou be able to lay down rules for others before thou shalt have first learned to obey rules thyself. Much more is this so in life.
In reading and writing thou must learn first to follow instruction before thou canst give it. Much more is this true of life.
Marcus Aurelius, Meditations XI.29. Translated by George Long (1862). The Stoic Library.