One of the main drivers behind programmatic’s meteoric growth (at least on the demand side) has been the ability to leverage data to find and buy specific users, out of seemingly infinite opportunities, wherever they might be online. After all, this enabling of “audience-based buying” brought marketers closer to their long-held notion of advertising utopia: reaching the right person, with the right message, at the right time, in the right context. It also, theoretically, went a long way to minimizing wasted ad spend and enabled significant performance gains. The ad dollars flowed. But this shift took its toll on the sell-side.