Why Rumors Spread
"Rumors have a way of slipping under our mental defenses before we think to question them. The best ones sidestep common sense entirely...Most of us don't like to think of ourselves as gullible. But we're especially likely to accept as true—and do our best to spread—tales that have several specific characteristics that take aim at our best defenses...
"1: Successful rumors needle our anxieties and emotions...Fear breeds rumor. The more collective anxiety a group has, the more inclined it will be to start up the rumor mill...we pass rumors around primarily as a means of deciphering scary, uncertain situations. Exchanging information, even if it's ludicrously false, relieves our unease by giving us a sense that we at least know what's happening...
"2: Rumors stick if they're somewhat surprising but still fit with our existing biases....If you already think liberals are waging a war on religion, you'll be more likely to buy 2008's (untrue) rumor that the new dollar coins omit the customary "In God We Trust." (It's printed along the side.)...Even when presented with evidence refuting a rumor, we often stick to our biases...
"3: Easily swayed people are more important than influential people in passing on a rumor...."It's your willingness to pass things along that matters"... Kids will believe almost anything (another long-lived schoolyard rumor claimed the "Mikey likes it" Life cereal kid died after a mixture of soda and Pop Rocks made his stomach explode), and thus rumors run rampant in schools. But the same is true of gullible adults: They're the ones who really fuel rumors...
"4: The more you hear a rumor, the more you'll buy it—even if you're hearing that it's false....
"5: Rumors reflect the zeitgeist...Rumors have the greatest chance of multiplying when the topic is something people are already pondering...
"6: Sticky rumors are simple and concrete....Examine your stockpile of offbeat conventional wisdom...We only use 10 percent of our brains. The Great Wall of China can be seen from space. People swallow eight spiders a year in their sleep. These tidbits are all simple and specific, with a vivid detail that sticks in the mind. They're also false. But they illustrate the point that tangible, easily graspable tales have an excellent chance of catching on...
"7: Rumors that last are difficult to disprove....Why do people still believe there's a giant prehistoric reptile prowling Loch Ness, even though innumerable hours of investigation have produced zero proof of such a creature? Well, it's a pretty big lake: How can we be sure she's not in there? It's tough to disprove the idea definitively...
"8: We are eager to believe bad things about people we envy.... Once someone hits a certain level of celebrity and adulation, it seems, the mill starts to churn automatically—and the more beautiful and successful the star, the more depraved the rumors. Jamie Lee Curtis is a hermaphrodite. Cher (or Janet Jackson) had a rib removed so she'd look skinnier. Catherine the Great died trying to make love to a horse..."
Some of these read like a manual for marketers.
Read more in this Psychology Today article.