Sed iniustitiæ genera duo sunt, unum eorum, qui inferunt, alterum eorum, qui ab is, quibus infertur, si possunt, non propulsant iniuriam. Nam qui iniuste impetum in quempiam facit aut ira aut aliqua perturbatione incitatus, is quasi manus afferre videtur socio; qui autem non defendit nec obsistit, si potest, iniuriæ, tam est in vitio, quam si parentes aut amicos aut patriam deserat.
But with respect to injustice there are two types: men may inflict injury; or else, when it is being inflicted upon others, they may fail to deflect it, even though they could. Anyone who makes an unjust attack upon a fellow human being, whether driven by anger or by some other perturbation, seems to be laying hands, so to speak, upon another human being. But also, he who fails to defend a fellow human being, or to obstruct injustice when it is within his power to do so, he is at fault just as if he had abandoned his parents or his friends or his country.
—Marcus Tullius Cicero, De Officiis lib. i, sec. 23 (44 BCE) (S.H. transl.)