Contagious Why Things Catch On

make the private public.
They figured out how to take support for an abstract cause—something not typically observable—and
make it something that everyone can see. For the thirty days of November people who sport a
moustache effectively become walking, talking billboards for the cause. As noted on Movember’s
website,
Through their actions and words they [participants] raise awareness by prompting private
and public conversations around the often-ignored issue of men’s health.
And start conversation it does. Seeing someone you know suddenly sprout a moustache generates
discussion. People usually gossip a bit among themselves until someone gets up the courage to ask the
wearer what prompted the new facial hair. And when he explains, he shares the social currency and
generates new devotees. Each year I see more and more of my students sporting moustaches come
November. Making the cause public helped it catch on more quickly than it ever could have
otherwise.
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Most products, ideas, and behaviors are consumed privately. What websites do your coworkers
like? Which ballot initiatives do your neighbors support? Unless they tell you, you may never know.
And though that might not matter to you personally, it matters a lot for the success of organizations,
businesses, and ideas. If people can’t see what others are choosing and doing, they can’t imitate them.
And, like the binge-drinking college students, people might change their behavior for the worse
because they feel their views aren’t supported.
*
Solving this problem requires making the private public. Generating public signals for private
choices, actions, and opinions. Taking what was once an unobservable thought or behavior and

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transforming it into a more observable one.
Koreen Johannessen was able to reduce Arizona students’ drinking by making the private public.
She created ads in the school newspaper that merely stated the true norm. That most students had only
one or two drinks, and 69 percent have four or fewer drinks, when they party. She didn’t focus on the
health consequences of drinking, she focused on social information. By showing students that the
majority of their peers weren’t bingeing, she helped them realize that others felt the same way. That
most students didn’t want to binge. This corrected the false inferences students had made about
others’ behavior and led them to reduce their own drinking as a result. By making the private public,
Johannessen was able to decrease heavy drinking by almost 30 percent.
ADVERTISING ITSELF: SHARING HOTMAIL WITH THE WORLD
One way to make things more public is to design ideas that advertise themselves.
On July 4, 1996, Sabeer Bhatia and Jack Smith introduced a new e-mail service called Hotmail. At
the time, most people got their e-mail through Internet service providers like AOL. You’d pay a
monthly fee, dial up from home using a phone line, and access your messages through the AOL
interface. It was restricting. You could connect only from the place where you had the service
installed. You were chained to one computer.
But Hotmail was different. It was one of the first Web-based e-mail services, which allowed
people to access their inbox from any computer anywhere in the world. All they needed was an
Internet connection and a Web browser. Independence Day was chosen for the announcement to
symbolize how the service freed people from being locked into their current provider.
Hotmail was a great product, and it also scored well on a number of the word-of-mouth drivers
we’ve talked about so far. At the time, it was quite remarkable to be able to access e-mail from
anywhere. So early adopters liked talking about it because it gave them Social Currency. The product
also offered users significant benefits over other e-mail services (for starters, it was free!), so many
people shared it for its Practical Value.
But the creators of Hotmail did more than just create a great product. They also cleverly leveraged
observability to help their product catch on.
Every e-mail sent from a Hotmail account was like a short plug for the growing brand. At the
bottom was a message and link that simply said “Get Your Private, Free E-mail from Hotmail at
www.hotmail.com
.” Every time current Hotmail customers sent an e-mail, they also sent prospective
customers a bit of social proof—an implicit endorsement for this previously unknown service.
And it worked. In a little over a year Hotmail signed up more than 8.5 million subscribers. Soon
after, Microsoft bought the burgeoning service for $400 million. Since then more than 350 million
users have signed up.
Apple and BlackBerry have adopted the same strategy. The signature lines at the bottom of their e-
mails often say “Sent using BlackBerry” or “Sent from my iPhone.” Users can easily change this
default message to something else (one of my colleagues changed his signature to say “Sent by Carrier
Pigeon”), but most people don’t, in part because they like the Social Currency the notes provide. And
by leaving these notes on their e-mail, people also help spread awareness about the brand and
influence others to try it.
—————
All these examples involve products that