They say some stories are too good to be true - although that has never stopped Hollywood.
The Devil's Double is the latest blockbuster to stretch the limits of the phrase "based on a true story".
But who cares, if it tells the gory tale of one of the most brutal psychopaths of the late 20th century?
The film, directed by New Zealander Lee Tamahori, recounts the knuckle-whitening autobiography of Latif Yahia, the supposed body double to Saddam Hussein's psychotic younger son, Uday.
British actor Dominic Cooper has won critical acclaim for his portrayal of a man who raped and murdered his way through Baghdad's high society - and also that of the poor sap who had to pretend to be such a maniac to protect him from the bullets of any would-be assassin.
In recent years, though, growing numbers of Uday's inner circle have cast doubt on whether the story could be feasible, though none of the doubters concern Tamahori.
"Biopics are not my favourite movies because they always try to steer too close to the facts," he writes.
"But the truth doesn't set you free in movies. Truth layered with fiction sets you free."
With a strikingly similar face to Uday - who was gunned down by American special forces alongside his brother Qusay in July 2003 - Yahia emerged in Europe in the early 1990s with a remarkable claim that generated headlines around the world.
He told intelligence agents he had lived a life of servitude as Uday's body double - and had turned on his master when Uday tried to kill him because a girlfriend had become overly flirtatious. Memoirs and international fame quickly followed.
According to his book, blog and media interviews, he was born into a wealthy family with close ties to Saddam's Ba'athist regime.
Part of Baghdad's elite, he went to the same school as Uday, where friends commented on how similar in appearance he was to the Iraqi dictator's sadistic youngest son.
In September 1987 during the Iran-Iraq war, he was called back from the frontlines and told to go to Saddam's Baghdad palace, he has said.
Uday had decided to make him a body double. When Yahia politely refused he was put in prison for a week and tortured.
Upon his release he was told that unless he agreed to become Uday's doppelganger his family would be killed and his sisters raped.
After rounds of plastic surgery, the transformation was complete.
Yahia said between 1987 and 1991 he was witness to some of Uday's worst excesses - his prowls through Baghdad at night looking for women to rape, his drug abuse, violent outbursts and penchant for torture. He also claims to have survived 12 attempted assassinations.
Yahia thought of escaping after Uday, angry that a girlfriend had started to openly flirt with the doppelganger, tried to shoot him.
Yahia claims he fled to Kurdish rebels in northern Iraq and later to Austria with the help of the CIA.
Yet some of those in Uday's inner circle at the time have poured scorn on Yahia's claims. Haytham Ajmaya, a 48-year-old Iraqi expat living in London, is one of them.
He defected from Iraq in 1998 with the help of the British Government in exchange for information on Uday's inner circle, within which he had served for more than a decade.
"Latif may have looked like Uday and talked like him but he was never Uday's body double," he said.
"It's a real shame that Hollywood has decided to make a film based on rubbish rather than a film that is true to Iraq's history."
Ajmaya claims that Yahia was someone who used his close resemblance to Uday to secure money and girls in Iraq and was in fact arrested by police for doing just that.
In January, a writer from the Sunday Times tracked down a further three members of Uday's inner circle who cast doubt on Yahia's claim, as well as Saddam's plastic surgeon, who said no operation had been carried out on a body double.
When confronted this year about the remarks by Uday's former friends, Yahia said: "I was Uday's double. Uday didn't have friends; he had pimps, drug dealers, hangers-on, etc. Either I am psychic to know about inside palaces, bunkers and all the rest of the places ... or I was actually there. I know the truth."
Toby Dodge, a historian at Queen Mary University of London, who has interviewed members of Saddam's regime, says that separating fact from fiction in Ba'athist Iraq is notoriously difficult.
"The regime had always been shrouded in mythology."