The four most dangerous words in finance are "this time is different". Thanks to this masterpiece by Carmen Reinhart of the university of Maryland and Kenneth Rogoff of Harvard, no one can doubt this again.

As the authors note, "If there is one common theme to the vast range of crises we consider in this book, it is that excessive debt accumulation, whether it be by government, banks, corporations or consumers, often poses greater systemic risks than it seems [to do] during a boom".