Find good teachers, then become one. Seneca, Epistles 3.25.4-7

Proper development of moral character requires some interaction with others. You cannot learn it by refusing to engage society. While the ethics of a crowd are not safe to imbibe or imitate wholesale, neither is the aspiring philosopher well-advised to run carelessly after whatever his personal tastes dictate, when he is alone. You can wreck with the group, on its terms, and alone, on yours. Temperance is learned as you consciously avoid the wreck, however that happens: it is generally easier to begin with help from those around you. Find the right teachers! Then, become your own teacher.


Tu nobis te, ut facis, fortem praesta et sarcinas contrahe; nihil ex his quae habemus necessarium est. Ad legem naturae revertamur; divitiae paratae sunt. Aut gratuitum est quo egemus, aut vile: panem et aquam natura desiderat. Nemo ad haec pauper est, intra quae quisquis desiderium suum clusit cum ipso Iove de felicitate contendat, ut ait Epicurus, cuius aliquam vocem huic epistulae involvam. Prodest sine dubio custodem sibi imposuisse et habere quem respicias, quem interesse cogitationibus tuis iudices. Hoc quidem longe magnificentius est, sic vivere tamquam sub alicuius boni viri ac semper praesentis oculis, sed ego etiam hoc contentus sum, ut sic facias quaecumque facies tamquam spectet aliquis: omnia nobis mala solitudo persuadet. Cum iam profeceris tantum ut sit tibi etiam tui reverentia, licebit dimittas paedagogum: interim aliquorum te auctoritate custodi, aut Cato ille sit aut Scipio aut Laelius aut alius cuius interventu perditi quoque homines vitia supprimerent, dum te efficis eum cum quo peccare non audeas. Cum hoc effeceris et aliqua coeperit apud te tui esse dignatio, incipiam tibi permittere quod idem suadet Epicurus: tunc praecipue in te ipse secede cum esse cogeris in turba. Dissimilem te fieri multis oportet. Dum tibi tutum non sit ad te recedere, circumspice singulos: nemo est cui non satius sit cum quolibet esse quam secum. Tunc praecipue in te ipse secede cum esse cogeris in turba; si bonus vir, si quietus, si temperans. Alioquin in turbam tibi a te recedendum est: istic malo viro propius es. Vale.


As for yourself: be strong for us, as is your custom, and cast off the material burdens that weigh you down. None of the things we possess is necessary. Let us return to the law of nature. Her wealth is already there for us, already ours. Anything we lack is either superfluous, or easy to come by. Nature desires only bread and water. Nobody is too poor for these things, and anyone who desires nothing more is vying with Jove when it comes to achieving happiness, as Epicurus remarks. I shall add his voice to this epistle, as to others. It is definitely beneficial to impose on yourself a guardian whose opinion you hold close, someone you can respect, someone whom you regard as a meaningful reference for your own thoughts. An even better recipe for greatness is living beneath the gaze of a good man who is always spending time in your presence, but I am content here with a half-measure: that you act in every case as though somebody were watching. Solitude urges us to every sort of evil. Only when you have learned to respect yourself properly will you be safe to dismiss your guardian and teacher. Meanwhile, as you build yourself into the kind of man in whose company you would not dare to sin, fortify your position with the authority of others—be it Cato, or Scipio, or Laelius (†), or someone else whose intervention has assisted lost men in overcoming their vices. Once you have achieved sufficient personal worship or honor, enough that you begin to respect your own opinion of yourself, then I will allow you to practice the habit Epicurus recommends: “When forced to be in a crowd, then especially you should withdraw into yourself.” It is right that you become different from the crowd. But as long as it is not yet safe for you to withdraw into yourself, regard the individuals you know: there is not a single one but would be better off in others' company, however indifferent, than on his own. “Withdraw into yourself most when you are forced to be in a crowd.” This works if you are a good man, quiet and self-regulating. Otherwise, you must flee solitude, withdrawing from it into the crowds, as cultivating your own company puts you too close to a bad man. Farewell.


---
() Seneca has mentioned these Roman heroes before (cf. 1.7 & 1.11; the proximity of Laelius suggests that the Scipio meant here is the most famous Africanus, victor at Zama).