^* That didn’t mean FBX’s marginal contribution to FB revenue was as dramatic as the difference in bid. Like most online ad auctions, Facebook ran a “second price” auction. The economic specifics are PhD level, but essentially it meant you paid the amount of the next-highest bid, rather than what you bid. If one did the math, it meant a much better price-discovery mechanism overall. To truly increase total revenue, you needed a density of bids at the “clearing price” the ad impression had sold for, pushing the aggregate prices paid upward. No density, and all those high bids did nothing for the bottom line. So our goal was to increase the overlap between outside FBX bidding interest and the ads volume FB brought to market. That’s what obsessed us on the FBX team.