Those two fatal words, Mine and Thine.

Miguel de Cervantes (1547-1616) Spanish novelist

Don Quixote, Part 1, Book 2, ch. 11 (1605) [tr. Motteux & Ozell (1743)]
    (Source)

Alt trans.:

• "Oh happy age, which our first parents called the age of gold! not because gold, so much adored in this iron-age, was then easily purchased, but because those two fatal words, mine and thine, were distinctions unknown to the people of those fortunate times." [Full version of the above]
• "Happy the age, happy the time, to which the ancients gave the name of golden, not because in that fortunate age the gold so coveted in this our iron one was gained without toil, but because they that lived in it knew not the two words 'mine' and 'thine'!" [tr. Ormsby (1885)]
• "Happy age, and happy days were those, to which the ancients gave the name of golden; not, that gold, which in these our iron-times, is so much esteemed, was to be acquired without trouble, in that fortunate period; but, because people then, were ignorant of those two words MINE and THINE." [tr. Smollett (1976), as Part 1, Book 1, ch. 3]