Contagious Why Things Catch On

The New York Times
for
more than a decade. With an eye for quirky topics and a deft narrative style, Grady won numerous
journalism prizes by making esoteric topics accessible to lay readers.
That day, one of Grady’s articles rocketed up the newspaper’s Most E-Mailed list. Within hours of
its publication thousands of people had decided to pass on the article to their friends, relatives, and
coworkers. Grady had scored a viral hit.
The topic? How fluid and gas dynamic theories were being used in medical research.
Grady’s article detailed something called schlieren photography, in which “a small, bright light
source, precisely placed lenses, a curved mirror, a razor blade that blocks part of the light beam and
other tools make it possible to see and photograph disturbances in the air.”
Sounds less than riveting, right? Join the club. When we asked people what they thought of this
article on a number of different dimensions, the scores were pretty low. Did it have lots of Social
Currency? No, they said. Did it contain a lot of practically useful information (something we’ll
discuss in the Practical Value chapter)? No again.
In fact, if you’d gone down the checklist of characteristics traditionally believed to be
prerequisites for viral content, Grady’s article, entitled “The Mysterious Cough, Caught on Film,”
would have lacked most of them. Yet Grady’s piece clearly had something special or so many people
wouldn’t have hit the e-mail button. What was it?
—————
Grady’s interest in science started in high school. She was sitting in chemistry class when she read
about Robert Millikan’s famous experiment to determine the charge on a single electron. It was a
complicated idea and a complicated experiment. The study involved suspending tiny droplets of oil
between two metal electrodes, then measuring how strong the electric field had to be in order to stop
the droplets from falling.
Grady read it several times. Again and again until she finally understood. But when she did, it was
like a flash going off. She got it. It was thrilling. The thinking behind the experiment was so clever,
and being able to grasp it was enthralling. She was hooked.
After school Grady went to work at 
Physics Today
magazine. Eventually she worked at 
Discover
and 
Time
magazine and finally worked her way up to health editor at 
The New York Times.
The goal
of her articles was always the same: to give people even just a little bit of that excitement that she had
felt back in chemistry class decades before. An appreciation for the magic of scientific discovery.
In her piece that October, Grady described how an engineering professor used a photographic
technique to capture a visible image of a seemingly invisible phenomenon—a human cough. The
schlieren technique had been used for years by aeronautics and military specialists to study how
shock waves form around high-speed aircraft. But the engineering professor had harnessed the
technique in a new way: to study how airborne infections like tuberculosis, SARS, and influenza
spread.
It made sense that most people thought the article wasn’t particularly useful. After all, they weren’t
scientists studying fluid dynamics. Nor were they engineers trying to visualize complex phenomena.

---

And while Grady is one of the best science writers out there, it made sense that the general
population would tend to be more interested in articles about sports or fashion. Finally, while coughs
would certainly be a nice trigger to remind people of the article, cold and flu season tends to peak
around February, four months after the article was released.
Even Grady was bemused. As a journalist, she’s delighted when something she writes goes viral.
And like most journalists, or even casual bloggers, she’d love to understand why some of her pieces
get widely shared while others don’t.
But while she could make some educated guesses, neither she nor anyone else really knew why one
piece of content gets shared more than another. What made this particular article go viral?
—————
After years of analysis, I’m happy to report that my colleagues and I have some answers. Grady’s
2008 article was part of a multi-year study in which we analyzed thousands of