Technology has always been used as a memory aid, of course, but in past millenia, scratching on a clay tablet, writing with a fountain pen, and snapping a digital photo have all required an act of will. Humans had to choose what they would remember.

Now, in an age of ever-cheaper storage, the data committed to machine memory requires an act of will to delete. Storage is now so cheap, in fact, that it requires more effort to cull an e-mail inbox or photo gallery than it does to simply hold on to everything.

To get back to a default state of forgetfulness, Mayer-Schönberger offers an intriguing proposal: find simple ways to give data an expiration date.