Seneca, Letters to Lucilius
103.2 (tr. Richard M. Gummere):
You are wrong to trust the countenances of those you meet. They have the aspect of men, but the souls of brutes; the difference is that only beasts damage you at the first encounter; those whom they have passed by they do not pursue. For nothing ever goads them to do harm except when need compels them: it is hunger or fear that forces them into a fight. But man delights to ruin man.
Erras si istorum tibi qui occurrunt vultibus credis; hominum effigies habent, animos ferarum, nisi quod illarum perniciosus est primus incursus: quos transiere non quaerunt. Numquam enim illas ad nocendum nisi necessitas incitat; aut fame aut timore coguntur ad pugnam: homini perdere hominem libet.
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