The printing press and innovation.
From Steven Johnson's Where Good Ideas Come From: The Natural History of Innovation:
As many scholars have noted, Gutenberg’s printing press was a classic combinatorial innovation, more bricolage than breakthrough. Each of the key elements that made it such a transformative machine—the movable type, the ink, the paper, and the press itself—had been developed separately well before Gutenberg printed his first Bible. Movable type, for instance, had been independently conceived by a Chinese blacksmith named Pi Sheng four centuries before. But the Chinese (and, subsequently, the Koreans) failed to adapt the technology for the mass production of texts, in large part because they imprinted the letterforms on the page by hand rubbing, which made the process only slightly more efficient than your average medieval scribe. Thanks to his training as a goldsmith, Gutenberg made some brilliant modifications to the metallurgy behind the movable type system, but without the press itself, his meticulous lead fonts would have been useless for creating mass-produced Bibles.
An important part of Gutenberg's genius, then, lay not in conceiving an entirely new technology from scratch, but instead from borrowing a mature technology from an entirely different field, and putting it to work to solve an unrelated problem. We don't know exactly what chain of events led Gutenberg to make that associative link; few documentary records remain of Gutenberg's life between 1440 and 1448, the period during which he assembled the primary components of his invention. But it is clear that Gutenberg had no formal experience pressing grapes. His radical breakthrough relied, instead, on the ubiquity of the screw press in Rhineland winemaking culture, and on his ability to reach out beyond his specific field of expertise and concoct new uses for an older technology. He took a machine designed to get people drunk and turned it into an engine for mass communication.
And from Samuel Arbesman's The Half-Life of Facts:
It turns out that the printing press is far from simple. The technological innovations that Gutenberg developed were much more than the modification of a wine press and the addition of the idea of movable type. Gutenberg combined and extended a whole host of technologies and innovations from an astonishing number of areas, and that is what made his work so powerful. He used metallurgical developments to create metal type that not only had a consistent look (Gutenberg insisted on this), but type that could be easily cast, allowing whole pages to be printed simply at once. He used chemical innovations to create a better ink than had ever been used before in printing. Gutenberg even exploited the concept of the division of labor by employing a large team of workers, many of whom were illiterate, to churn out books at a rate never before seen in history. And he even employed elegant error-checking mechanisms to ensure that the type was always set properly: There was a straight line on one side of each piece of type so that the workers could see at a glance whether any letters had been set upside down.
Only by having the combined knowledge of all of these technologies does the printing press become possible and cost-effective.