Interesting to hear Alan Greenspan lay the blame for the scale of US troubles right at the door of the sub-prime idiocy. Since I commented on this, others have insisted it’s much more complicated than this – maybe , but don’t underestimate the power of that much misunderstood phenomenon – tipping points.

As commonly understood, and indeed as explained in Michael Gladwell’s popular book, it’s all about the take-off of self-reinforcing effects. But there’s a much more powerful source of tipping points – ...