For as in war many necessary things, otherwise bad, are customary and have as it were the sanction of law, so that they cannot be abolished in spite of the injury they do, so enmity drags along in its train hatred, and envy, and jealousy, and malignity, and revenge, and stamps them on the character.
 Plutarch, Moralia (c. 100 AD). copy citation

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Author Plutarch
Source Moralia
Topic revenge jealousy
Date c. 100 AD
Language English
Reference
Note Translated by Arthur Richard Shilleto
Weblink http://www.gutenberg.org/files/23639/23639-h/23639-h.htm

Context

“For he who praises another receives on that account greater praise himself, and is the more credited on another occasion when he finds fault, as not having any personal ill-feeling against the man, but only 211 disapproving of his act; and what is most noble and advantageous, the man who is accustomed to praise his enemies, and not to be vexed or malignant at their prosperity, is as far as possible from envying the good fortune of his friends, and the success of his intimates. And yet what practice will be more beneficial to our minds, or bring about a happier disposition, than that which banishes from us all jealousy and envy? For as in war many necessary things, otherwise bad, are customary and have as it were the sanction of law, so that they cannot be abolished in spite of the injury they do, so enmity drags along in its train hatred, and envy, and jealousy, and malignity, and revenge, and stamps them on the character. Moreover knavery, and deceit, and villainy, that seem neither bad nor unfair if employed against an enemy, if they once get planted in the mind are difficult to dislodge; and eventually from force of habit get used also against friends, unless they are forewarned and forearmed through their previous acquaintance with the tricks of enemies.” source