Ever since civilised society began, we have felt the need to classify, categorise and specialise. It can make things more efficient, and help give the leaders of any organisation a sense of confidence that they have the right people focusing on the right tasks. But it can also be catastrophic, leading to tunnel vision and tribalism. Most importantly it can create a structural fog, with the full picture of where an organisation is heading hidden from view.  Tett uses an anthropological lens to explore how individuals, teams and whole organisations often work in silos of thought, process and product. With examples drawn from a range of fascinating areas – from the New York Fire Department and Facebook to the Bank of England and Sony – these narratives illustrate not just how foolishly people can behave when they are mastered by silos but also how the brightest institutions and individuals can master them. Tett is US Managing Editor of the FT.