What Facebook offers advertisers that other news organizations do not, says Gans, is a quality he calls magnetism – limited content of high value, frequently renewed. Few readers remain on the site for very long. But they return to it regularly: they are faithful. And this creates a proposition that advertisers may find compelling. If they want to reach a large fraction of the US population over the next few days, Facebook may be the way to do it. The alternative is to purchase multiple digital impressions in many media, hoping to find the right eyeballs. Roughly speaking, this is what Facebook founder Mark Zuckerberg has done. He has assembled readers in order to sell their attention to advertisers – it’s a classic two-sided market, just like a newspaper or a television show, except that before Facebook, Gans says, “No one had figured out how to sell ads while your friends and family were talking to you.”

In Which, Finally, I Understand Facebook