In Delete, Mayer-Schönberger traces the history of such external memories – cave paintings, scrolls, photographic slides, diaries – and their importance to the flourishing of human knowledge. "Since the early days of humankind," he writes, "we have tried to remember, to preserve our knowledge, to hold on to our memories and we have devised numerous devices and mechanisms to aid us. Yet through millennia, forgetting has remained just a bit easier and cheaper than remembering."

No longer. Because of the digital revolution, he argues, it is easier to keep everything – the drunken email you sent your boss, the photo you put on Facebook in which you're doing something non-CV-enhancing to an inflatable cow – rather than go through the palaver of deciding what to consign to oblivion.

In 2006 Stacy Snyder, a 25-year-old student at Millersville University in Pennsylvania, was denied a teaching degree just days before graduation. University officials had discovered a photo of her, captioned “Drunken Pirate,” on MySpace. The photo showed Snyder wearing a pirate hat and drinking from a plastic cup, and the university accused her of promoting underage drinking. As Viktor Mayer-Schönberger tells the story in his new book Delete: The Virtue of Forgetting in the Digital Age, Snyder lost control over the photo when it was indexed by Google and other search engines: “the Internet remembered what Stacy wanted to have forgotten.”

Snyder’s story, and others like it, motivate Delete’s plea for “digital forgetting” (though it turned out that the university had other reasons to deny Snyder her certificate, including poor performance).