The daily and stubborn reality for everybody building businesses on the strength of Web advertising is that the value of digital ads decreases every quarter, a consequence of their simultaneous ineffectiveness and efficiency. The nature of people's behavior on the Web and of how they interact with advertising, as well as the character of those ads themselves and their inability to command attention, has meant a marked decline in advertising's impact.

original article: http://www.technologyreview.com/news/427972/the-facebook-fallacy/

I'm having trouble understanding what is meant by "efficiency of ads" and how that lowers ad value. I understand effectiveness, I think: users are habituated to ads and click/notice them less and less over time. Thus ads lose value. (Site operators can't charge advertisers as much)

But efficiency seems to be about targeting users more efficiently. How does efficiency lower ad value? It seems advertisers should be willing to pay more for more efficient ads?