Our brains don’t let piddling little facts get in the way of a good story, allowing lies to infect the mind with surprising ease.

If you ever need proof of human gullibility, cast your mind back to the attack of the flesh-eating bananas. In January 2000, a series of chain emails began reporting that imported bananas were infecting people with “necrotizing fasciitis” – a rare disease in which the skin erupts into livid purple boils before disintegrating and peeling away from muscle and bone.
According to the email chain, the FDA was trying to cover up the epidemic to avoid panic. Faced with the threat, readers were encouraged to spread the word to their friends and family.
The threat was pure nonsense, of course. But by 28 January, the concern was great enough for the US Centers for Disease Control and Prevention to issue a statement decrying the rumour.
Did it help? Did it heck. Rather than quelling the rumour, they had only poured fuel on its flames. Within weeks, the CDC was hearing from so many distressed callers it had to set up a banana hotline. The facts became so distorted that people eventually started to quote the CDC as the source of the rumour. Even today, new variants of the myth have occasionally reignited those old fears.

We may laugh at these far-fetched urban myths – as ridiculous as the ongoing theory that Paul McCartney, Miley Cyrus and Megan Fox have all been killed and replaced with lookalikes. But the same cracks in our logic allow the propagation of far more dangerous ideas, such as the belief that HIV is harmless and vitamin supplements can cure AIDS, that 9/11 was an ‘inside job’ by the US government, or that a tinfoil hat will stop the FBI from reading your thoughts.

Why do so many false beliefs persist in the face of hard evidence? And why do attempts to deny them only add grist to the rumour mill? It's not a question of intelligence – even Nobel Prize winners have fallen for some bizarre and baseless theories. But a series of recent psychological advances may offer some answers, showing how easy it is to construct a rumour that bypasses the brain’s deception filters.

One, somewhat humbling, explanation is that we are all “cognitive misers” – to save time and energy, our brains use intuition rather than analysis......

....Consider the questions of whether others believe a statement or not, and whether the source is credible. We tend to trust people who are familiar to us, meaning that the more we see a talking head, the more we will begrudgingly start to believe what they say. “The fact that they aren’t an expert won’t even come into our judgement of the truth,” says Newman. What’s more, we fail to keep count of the number of people supporting a view; when that talking head repeats their idea on endless news programmes, it creates the illusion that the opinion is more popular and pervasive than it really is. Again, the result is that we tend to accept it as the truth....
....Lab experiments confirm that offering counter-evidence only strengthens someone’s conviction....
http://www.bbc.com/future/story/20160323-why-are-people-so-incredibly-gullible