Recessions are part of human nature, says Reserve Bank Governor Glenn Stevens [pdf]:
No country has managed to eliminate the business cycle. No country ever will, because the cycle is driven by human psychology, which finds expression in financial behaviour as well as ‘real’ behaviour. We are seemingly just made – ‘hardwired’, as some would put it – in a way that makes us prone to bouts of optimism and pessimism. Occasionally, we are prone to periods of myopic disregard for risk followed, in short order, by an almost complete unwillingness to accept risk. [p. 2]
‘Behavioural finance’ is one of the new big things in economics. It ditches the assumption of rationality but keeps the methodological individualism.
Better explanations for booms and busts ditch the methodological individualism, and it follows from that that psychological states don’t matter so much. Rationality we can actually keep, but (1) bureaucratic rather than personal rationality, (2) embodied in a variety of fundamentally different kinds of institution, and (3) bearing in mind that ‘rationality’ does not mean ‘omniscience’ and certainly not ‘knowledge of the future’. (The last might go without saying, but the term has slipped a long way in economic theory.)