Facebook says roughly one in seven people on the planet log in at least once a month. And yet, how News Feed works remains bafflingly opaque, like a secret box of technology, algorithms and magic that remains one of tech’s bigger mysteries. An entire consulting industry is built around trying to game it (think SEO for Google), and publishers invest enormous amounts of energy into succeeding on it, but as soon as people start to figure it out Facebook tweaks its secret recipe and everything goes out the window.