The Roman playwright Titus Maccius Platus (254–184 BC) is first credited with the phrase ‘Homo homini lupus’ (man is a wolf to man). Arthur Schopenhauer used the phrase in his book The World as Will and Representation, and Sigmund Freud utilized such a phrase in the passage below:
“The bit of truth behind all this – one so eagerly denied– is that men are not gentle, friendly creatures wishing for love, who simply defend themselves if they are 
attacked, but that a powerful measure of desire for aggression has to be reckoned as part of their instinctual endowment…Homo homini lupus [man is a wolf to man], who has the courage to dispute it in the face of all the evidence in his own life and in history? This aggressive cruelty usually lies in wait for some provocation, or else it steps into the service of some other purpose, the aim of which might as well have been achieved by milder measures. In circumstances that favor it, when those forces in the mind which ordinarily inhibit it cease to operate, it also manifests itself spontaneously and reveals men as savage beasts to whom the thought of sparing their own kind is alien.”(Sigmund Freud)
As the philosopher Joseph de Maistre (1753-1821) alludes to below, echoing Freud, man is man’s own worst enemy:
“Man’s destructive hand spares nothing that lives; he kills to feed himself, he kills to clothe himself, he kills to adorn himself, he kills to attack, he kills to defend himself, he kills to instruct himself, he kills to amuse himself, he kills for the sake of killing. Proud and terrible king, he wants everything and nothing resists him… from the lamb he tears its guts and makes his harp resound… from the wolf his most deadly tooth to polish his pretty works of art; from the elephant his tusks to make a toy for his child – his table is covered with corpses… And who [in this general carnage] will exterminate him who exterminates all others? Himself. It is man who is charged with the slaughter of man.” (Joseph de Maistre)
