* Illustration: Fry Pappy * Have we forgotten how to forget? Viktor Mayer-Schönberger worries about this. The associate professor of public policy, who is affiliated with Harvard, has written a fascinating book called Delete: The Virtue of Forgetting in the Digital Age, due out in September. In it, he argues that technology has inverted our millennia-old relationship with memory.

For most of human history, almost everything people did was forgotten, simply because it was so hard to record and retrieve things. But there was a benefit: "Social forgetting" allowed everyone to move on from embarrassing or ill-conceived moments in their lives.

Digital tools have eliminated that amnesty. Google caches copies of our blog postings; social-networking sites thrive by archiving our daily dish. Society now defaults to a relentless Proustian remembrance of all things past.

The downsides are obvious. We live with a nagging fear that something we say or do online will come back to haunt us years later. (Just ask anyone who's been Google-vetted at the start of a relationship.) "We become enormously more cautious with what we say or do," says Mayer-Schönberger. And society suffers when people stop taking risks.

So what's the solution? Mayer-Schönberger argues that we need to stop creating tools that automatically remember everything. Instead, we need to design them to forget.

As it turns out, software developers are beginning to do just that: They're becoming architects of oblivion. A good example is Drop.io. It's one of many new "private sharing" services that let you upload a file—a picture, a video, whatever—and get a special URL you can give to select friends or workmates. Photographers, for instance, use it to send photos to clients when they want to keep the images under wraps.

But here's what makes Drop.io unique: When you upload a file, the service asks you to put an expiration date on it. It could be a month, a few hours, even "after five people have seen it." If you don't set a date, the default is one year. And when that time arrives, the file is deleted.

The result? Of the tens of millions of files uploaded to Drop.io in the past year and a half, two-thirds no longer exist. As company founder and CEO Sam Lessin says, Drop.io files are "like little wormholes that pop into and out of existence for a specific purpose."

Another case of intentional forgetting is the Guest Pass feature on Flickr. Like Drop.io, it lets you share a specified photo stream by creating dedicated URLs that you can email to friends. And with one click you can "expire" those links. According to senior engineer Kellan Elliott-McCrea, about 11 percent of all Flickr members use Guest Pass, mostly for snapshots of kids, homes, weddings, and parties. That's precisely the kind stuff you want to show off, while retaining the ability to make it go poof*.*

Of course, there are no guarantees. Someone could take a private file they've been granted temporary access to and re-post it for all to see, forever. But because these systems have been engineered for forgetting, users tend to respect this. Our behavior is shaped by the code.

Mayer-Schönberger thinks all social software should be designed like Drop.io—to at least ask when we want our posts and uploads to be deleted. That way, we'd be more inclined to meditate for a second about whether something ought to live forever. Because in a world of cheap data storage, if we're not prompted to delete, we won't. (By Mayer-Schönberger's calculation, the amount of flash RAM needed to store a photo costs less than the few seconds spent deleting it.)

Being required to think about whether to retain or discard a digital memory will have another side benefit: It will make us pay closer attention—in real time!—to our experiences. If you decide a sunset or a conversation is going to live only in your mind instead of on your hard drive, you'll probably savor it more richly. Just ask Marcel Proust.

Email clive@clivethompson.net.

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