We all know social media's genius at pretending to read our minds. Facebook and Google+ reintroduce us to our friends; Pandora plays us music we're algorithmically likely to enjoy; Amazon delivers us to authors who feel statistically familiar. This sleight of hand flatters us and pulls us inward.

But what it doesn’t do so well is surprise us. Our sense of serendipity—the startling coincidence, the amazing happenstance—has eroded severely. A random greeting from a long-lost friend once would have been a lightning bolt in your day; by now, it’s much tougher to lose touch with someone than get reacquainted. If your most discreet pals plot your surprise party, their presence in your location-based apps will give up the ghost. Want to go wander around a foreign city? Forget it: Google has made getting lost not just obsolete but technically impossible.

Will surprise be the next hot online commodity? We’ve seen signs that it might. Chatroulette’s randomness enthralled us briefly, and group-deal sites’ digital coupons deliver us the odd caipoeira lesson—but could surprise be more valuable than that? Will social media, or advertisers, figure out how to sell us back our serendipity?