Seneca, Moral Epistle 25.5-6
“Act in every way as if Epicurus were watching you.” It is certainly an advantage to get yourself a minder to consult, someone you consider an overseer for your thoughts. It is far better to live as if some noble man were always in your sight, but I am happy if you do what you do as if anyone else is watching–isolation commends every kind of evil to us.
When you have advanced so far that you are also embarrassed in front of yourself, then you can dismiss your witness. In the meantime, choose some other authority as a guardian for yourself, a Cato or Scipio or Laelius or any person whose presence would curb the offenses of even the worst kind of wastrel. Do this as long as it takes to make yourself the kind of person in whose presence you wouldn’t dare to sin.
When you have accomplished this and you begin to have real self-respect, I will start to let you do what Epicurus advises in another passage: “The best time to retreat within yourself is when you are compelled to be in a crowd.”
“Sic fac,” inquit, “omnia, tamquam spectet Epicurus.” Prodest sine dubio custodem sibi inposuisse 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 talis, cuius1 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.”