In 1703 a young man arrived in London who said he was a native of Formosa, the island now called Taiwan, that he had been brought to Europe by a Jesuit, and that he had escaped and converted to Anglicanism. He was blond and pale, which he explained by saying that Formosans of the upper class lived underground and were therefore fair.
He was a Frenchman, and nobody has ever established his real name. He took the name George Psalmanazar.
The Bishop of London took him up. He was presented to the Royal Society. In 1704 he published An Historical and Geographical Description of Formosa, which described a nation with a religion requiring the annual sacrifice of eighteen thousand boys' hearts, a diet including raw meat and serpents, a currency, a calendar, an architecture, and a complete alphabet and grammar of the Formosan language. He was sent to Oxford to teach it. The book was a bestseller and was translated.
Every word was invented, and he invented it fluently — he could speak and write his language extempore, consistently, for years, and produce the same forms when asked again months later.
Three mechanisms sustained this.
Confirmation bias in the sponsors. Psalmanazar's Formosa was constructed to fit what his English patrons already believed: it was a heathen society that had been corrupted by Jesuit missionaries, and its convert was now safely Anglican. Anti-Catholic clergymen with a theological interest in the story were not motivated to find holes in it, and they were the people best placed to find them.
Structural fluency as an authenticity cue. The invented alphabet was internally consistent, and consistency reads as evidence. Nobody in London could evaluate whether Formosan grammar was correct, so what they evaluated instead was whether it hung together, which it did — a processing-fluency judgment substituting for a factual one.
And the audience defending the story on his behalf. His complexion was the obvious objection, and he did not have to answer it; his supporters produced the underground-living explanation and repeated it. Edmond Halley questioned him about the sun's position and the length of shadows in Formosa, and caught inconsistencies. Father Candidius's genuine earlier account of the island contradicted him throughout. Neither settled anything, because the people invested in the story generated repairs faster than the critics generated objections.
He gave it up eventually and lived out a long life as a hack writer and Hebrew scholar, becoming a friend of Samuel Johnson, who reportedly said he would as soon think of contradicting a bishop. He confessed in a memoir published after his death in 1763.
The general finding is the uncomfortable one. Psalmanazar's fraud did not survive because it was well constructed, though it was. It survived because the people who could have destroyed it were the people who wanted it to be true, and they did his defensive work for him.