The world of public intellectuals has been replaced by an inferior mob of "thought leaders", says Daniel Drezner in his new book The Ideas Industry. These thinkers, rather than examining the world as it is, tend to push "big ideas" with unscientific bases that catch the public imagination. For example, in his book The Outliers, Malcolm Gladwell convinced the world that every skill requires 10,000 hours of practise to master, but a scientific study showed no evidence for this. Gladwell's magic number is, like many "big ideas", tantalising and entertaining, but a bad basis for any actual societal decisions.