It means to give credit to the author and source. It helps in an argument because when you're trying to prove a point, you have to have factual evidence that proves you're right.
The moral of Guy de Maupassant’s “The False Gems” (“Les Bijoux” in French, 1883) sharply questions the hypocrisy of its male protagonist, Monsieur Lantin. Lantin is passionately in love with his young wife, whom he sees as the embodiment of beauty and virtue. His wife is perfect in every aspect, except for her love of imitation jewelry and the theater. Being of a puritanical bent of mind, Lantin finds both of his wife’s interests showy and improper. Clearly, such interests do not fit his worldview of what a well-brought-up, modest woman should be enjoying. At one point he remonstrates her ostentatious tastes, saying:
My dear, as you cannot afford to buy real diamonds, you ought to appear adorned with your beauty and modesty alone, which are the rarest ornaments of your sex.
Clearly, it is not the fact that she wears jewelry which bothers Lantin, but the fact that these gems are false. Despite having such fixed notions about real and fake, truth and deception, Lantin is ironically oblivious to how his wife manages to eke out their lavish lifestyle on his modest salary of 3,500 francs. After his wife dies of a lung infection, Lantin is heartbroken. But soon the heartbreak is replaced by financial hardship: left to manage his income by himself, Lantin struggles for even his next meal. Here, he commits his first act of impropriety, attempting to sell off his beloved wife’s imitation jewelry. Thus, the text begins to reveal his hypocrisy.
When a jeweler’s appraisal shockingly reveals that the ornaments are not fake at all, but real and precious, Lantin’s hypocrisy sparkles as well. At first, he falls into a “dead faint” at the implication of the jewelry's actual worth. His modest, virtuous wife was clearly leading a double life, being gifted gems from her many admirers. It was this double life that funded the extravagant lifestyle of the Lantins.
But Lantin’s state of shock at his wife’s “betrayal” does not last long and gives way to something else quickly enough. Instead of shunning the income, which should be deemed dubious by his strict standards, he sells off all the jewelry, resigns from his job, and settles into a life of leisure. In this, the story exposes Lantin’s hypocrisy completely. His love for his wife perishes with her “deception,” but he is not above enjoying the fruits of her lies. He even discovers a love for the theater, for which he harshly judged his late wife. And soon enough he remarries, but in a cunning twist, the effect is not what he had hoped.
Six months afterward he married again. His second wife was a very virtuous woman, with a violent temper. She caused him much sorrow.
As we see, the story challenges Lantin’s definitions of truth, happiness, and virtue in a wife; and he gets his just desserts for his double standards. The wife he considered “impure” was the one he was truly happy with, while the truly virtuous woman causes him “much sorrow,” as he deserves.
