That is because they are designed assuming rational behaviour, whereas markets have a nasty tendency to react unpredictably.

ECONOMIST: Financial markets: Copy the lowly cockroach | The

The other thing is that the 20th century did not stand out as a century in which rational behaviour triumphed.

BBC: News | Back to the future | John Mohawk

He and Morgenstern may have been the first to show how the philosophical idea of rational behaviour could be applied to economics.

ECONOMIST: John Harsanyi

There are some exceptions: much effort has recently gone into examining non-rational or nearly rational behaviour in special contexts, often with interesting results.

ECONOMIST: The benevolence of self-interest | The

Mr Chancellor is right to say that some economists have tried too hard to explain everything from the tulip mania onwards as rational behaviour.

ECONOMIST: Financial speculation

Much of modern macroeconomics has been about how, and whether, his ideas fit into the formal microeconomic building blocks of rational behaviour and complete markets.

ECONOMIST: John Maynard Keynes

This is not sane or rational behaviour.

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Emotions have far more effect on buying behaviour than rational messaging.

FORBES: Creativity Sells.

And it was, as we now know from Alistair Darling, on the point of making that cameraman's behaviour entirely rational: the ATMs were "hours away" from shutting down.

BBC: Tick, tock: The risks of depositor flight in Greece

Behaviour that may be rational for individual actors can cause chaos if everyone copies it.

ECONOMIST: Cotton exports