How few philosophers are to be found who are such in character, so ordered in soul and in life, as reason demands; who regard their teaching not as a display of knowledge, but as the rule of life; who obey themselves, and submit to their own decrees!

[Quotus enim quisque philosophorum invenitur, qui sit ita moratus, ita animo ac vita constitutus, ut ratio postulat? qui disciplinam suam non ostentationem scientiae, sed legem vitae putet? qui obtemperet ipse sibi et decretis suis pareat?]

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

Tusculan Disputations [Tusculanae Disputationes], Book 2, ch. 4 (2.4) / sec. 11 [Marcus] (45 BC) [tr. Peabody (1886)]
    (Source)

Original Latin. Alternate translations:

For where is there one Philosopher of a thousand to be found, of such a Temper and Conversation, as Reason requires? who maketh use of his Doctrine not for Ostentation of Knowledge, but a Rule of Life? who believes himself, and observes his own Precepts?
[tr. Wase (1643)]

For how few philosophers will you meet with, whose life and manners are conformable to the dictates of reason? who look on their profession, not as a means of displaying their learning, but as a rule for their practice? who follow their own precepts, and comply with their own decrees?
[tr. Main (1824)]

For, how rare to find a philosopher with such morals, with a mind and life so regulated, as reason requires -- who deems his own doctrine, not a parade of science, but the rule of life -- who yields obedience to himself, and deference to his own decrees.
[tr. Otis (1839)]

For how few philosophers will you meet with, whose life and manners are conformable to the dictates of reason! who look on their profession, not as a means of displaying their learning, but as a rule for their own practice! who follow their own precepts, and comply with, their own decrees!
[tr. Yonge (1853)]