If a house of cards collapses it happens either because of its own weight and instability or because of an external force – a nudge, a jolt, a passing breeze.
The conventional wisdom about the collapse of the house of cards that the banks built is that it’s the former. It’s purely down to greed – bankers building an unsustainable edifice of funny money with their CDOs, CDSs and other fancy derivatives, one that inevitably came crashing down around their ears.