Naivety

The 1929 crash exposed the naivety and ignorance of bankers, businessmen, Wall Street experts and academic economists high and low; it showed they did not understand the system they had been so confidently manipulating. They had tried to substitute their own well-meaning policies for what Adam Smith called ‘the invisible hand’ of the market and they had wrought disaster. Far from demonstrating, as Keynes and his school later argued—at the time Keynes failed to predict either the crash or the extent and duration of the Depression—the dangers of a self regulating economy, the degringolade indicated the opposite: the risks of ill-informed meddling.

Paul Johnson in Modern Times. I doubt that the G20 has done any better.