They were afraid that everything would be lost.

Their community in northwestern China, along the Silk Road, was under threat from a neighboring

group, so they gathered their most valuable possessions and walled them up inside a cave, and then

a thousand years passed by.

In 1900, a monk was exploring that very same cave when he encountered the hidden treasure,

but it wasn't gold or precious gems that he stumbled upon.

No, this hoard was a collection of over 40,000 scrolls and documents, a secret library

that archaeologists today refer to as the cave of a thousand Buddhas.

Among the seemingly endless collection of ancient scrolls was a document that is known today

as the Diamond Sutra.

It was printed in the year 868, according to the text on the document, making it the oldest

printed and dated book in the world.

But it's also the earliest example of one of the most common genres throughout history.

It is a How-To Guide.

We like to teach things.

It's how we pass along our knowledge to the next generation and how we grow as individuals.

Whether we're switching professions in the middle of a career or a young student who's

learning things for the first time, how two guides can transform lives and open up worlds

of possibility.

But everything useful has a darker underbelly.

Tools can be misused.

Weapons designed for hunting can be turned on helpless people, and books can contain

...