What do a $100 Philly cheese steak, the Movember movement and Rebecca Black's universally panned Friday video have in common?
The answer: They're all highly contagious. Whether we love them or loathe them, certain ideas, products, stories and YouTube videos become viral sensations as people just can't resist the urge to share them. But why do some things immediately take off, while others fall flat?
Jonah Berger, an assistant marketing professor at the Wharton School of the University of Pennsylvania, has spent more than a decade examining phenomena like the most widely shared New York Times articles, frumpy Susan Boyle's stunning debut on Britain's Got Talent and the uncanny popularity of those yellow Livestrong wristbands.
Berger shares his findings in his new book, Contagious: Why Things Catch On, providing fascinating insight into the science of social transmission. While conventional wisdom suggests that trends are spread by highly influential people, he argues that almost anything can be made viral by anyone.
We reached Berger by phone while he was travelling in Seattle. He explained how several key principles, such as social currency, triggers and observability, drive contagion.
What it is: "Just like the cars people drive and the clothes people wear, what people say affects how others see them. So people talk about things that make them look smart or in the know."
How it works: "Things that make people feel like insiders have valuable social currency. So when we have access to special information or maybe we've been invited to an early premiere of a movie, or we are able to try a restaurant before it opens, these scarce or exclusive experiences make us feel special. And so we talk about them because they make us look good."
The McRib phenomenon: "The McRib sandwich, made by McDonald's, is not real rib meat; it's made of less-delicious parts of the pig. While initial sales of the sandwich were okay, they weren't great. So McDonald's took a different marketing tactic, making it available only at certain times at certain stores. By making the McRib scarce, they actually increased sales and word-of-mouth. Whenever it was available at a given location, people wanted to share the news with others."
What they are: "We talk about things that are top of mind. What triggers – or cues in the environment – do is they make things top of mind. For example, if I said, 'Peanut butter and …,' you might say, 'Jelly.' Peanut butter is a trigger for jelly. It makes us think about jelly even though it's not there. So by reminding us about certain ideas, triggers cause those products or ideas to be discussed."
How they work: "Frequent triggers are the best. And you also need to think about the context. In Philadelphia, a luxury steakhouse called Barclay Prime triggered a lot of interest in the city with the introduction of a $100 cheese steak because Philadelphia is known for its cheese steaks [which ordinarily only cost a few dollars]. But in Toronto, for example, cheese steaks aren't as popular. Because of that, people are less likely to think about it and the story of the $100 cheese steak is less likely to be triggered."
The Rebecca Black phenomenon: "Friday was one of the most popular songs of 2011. Everyone hated the song and yet it had over 3 million views. Why is it so popular? When you look at the data, what you see is a spike in attention to the song every Friday. The song is equally bad on Monday, Tuesday, Wednesday, Thursday and Friday, but because Friday has the word 'Friday' in it, the day of the week reminds people that the song exists, causing them to talk about it and share it, and thus making it more successful."
What it is: "People tend to imitate others. But we can only imitate others if we can see what they're doing. When you're in a foreign city, for example, you often look at which restaurants are full and use that as a signal of quality. Is it busy? It must be good. But if the windows are frosted or there are no windows at all, you can't tell whether it's busy or empty, and so you're unlikely to go there. So the idea is to make the private public. When it's easier to see what other people are doing, it increases the chance that that thing will catch on."
The Movember phenomenon: "Donations are usually a private behaviour, so it's really hard for them to be contagious. With Movember, people get sponsored to grow a mustache for the month of November in support of men's cancers. What's great about this is mustaches are a really public signal. If you suddenly see a bunch of people sporting mustaches, you're going to ask about it. Along the way, you're learning more about the cause and it makes you more likely to donate as well and participate."
The 'Just Say No' phenomenon: "Making things public can lead to negative things catching on as well. Anti-drug campaigns, like 'Just Say No' commercials, tell people drugs are bad. But they also often suggest that other people are doing drugs – that the cool kids at school are going to ask you to use drugs and you should say, 'No.' Imagine you're a child sitting at home, and you're saying, 'Wow, I had no idea people were using drugs. And the cool kids are using drugs. Who knew? If they're doing it, it must be a good thing.'"
The bottom line: "Whenever you make the private public, you'll increase the chance that people imitate that behaviour. The question is, do you want that to happen? If you want to decrease an incidence of behaviour, like downloading illegal music or using drugs, you don't want to make it public."
This interview has been condensed and edited.