We have never in human history seen a run-up in credit of the kind we have just witnessed in advanced economies since 1970, and we have never observed modern finance-capitalist systems operating over a sustained period at this kind of credit-to-GDP leverage ratio.

It's just very hard to teach a class of students about what has happened in the Global Financial Crisis, how we ended up there and how we got to where we are today, without having some basic, non-trivial understanding of the financial sector, credit, and the banking system.

The basic aggregate measure of gearing or leverage is telling us that today's advanced economies' operating systems are more heavily dependent on private sector credit than anything we have ever seen before. Furthermore, this pattern is seen across all the advanced economies, and isn't just a feature of some special subset (e.g. the Anglo-Saxons).

We may end up with a world based more on equity than debt, or more on market debt instruments than bank intermediation but how and why we get there is a mystery. Absent significant regulatory or tax changes, and a sharp transition could be disruptive.