ABN sees a risk of iron ore will drop below $US40 a dry ton. Credit:Louis Douvis What happened was a huge jump in the world prices of coal and iron ore as China's period of rapid economic development of heavy industry and infrastructure caused global demand to outstrip global supply. The surge in China's demand caught the world's mining industry unprepared. Like miners in other countries, our largely foreign-owned miners lapped up the huge increase in prices and profits. But it didn't take long for greed ("the profit motive", if you prefer) and the irrational optimism that drives the world's entrepreneurs to take over, with firms seeking to exploit the high prices to the full by expanding their production capacity as much as possible as fast as possible. What then kicked off was a multi-billion dollar race - between rival firms in a country, but also with the many firms in other countries, all expanding their capacity as fast as they could.

It takes a long time to build new mines and bring them into production. So the chances of your mine being completed in time to enjoy the super-high prices aren't great - the more so because it's essentially a self-defeating process: the more firms join the race and the harder they try to be among the first to complete, the sooner supply catches up with demand and prices start falling. If mining firms were more rational, fewer would join the race. But firms are just as subject to herd behaviour as investors in a booming stockmarket. A mining chief who didn't join the comp would be subject to heavy criticism. This is where the irrational optimism comes in. Each individual entrepreneur is in no doubt he'll be among the race's winners. We're gonna make a motza. But while the miners are busy gearing up, their foreign customers are just as likely to be coming towards the end of their own boom in investment and construction. The inevitable result is that the global mining industry moves from a starting point of under-capacity to an end point of over-capacity. This is the eternal story of mining. Only in passing is it ever in equilibrium; it's almost always in either under- or oversupply - probably spending a lot more time over than under, the less profitable of the two conditions.

Now, this cycle isn't news to conventional economics, with its familiar "cobweb theorem" and "hog cycle" seeking to explain the phenomenon. But these models put too much of the blame on the unavoidable delays in increasing production, and too little on animal spirits. And they don't prepare us for all the waste and inefficiency involved in a resources boom. In the miners' race to be first in and best dressed they compete furiously for resources, bidding up hugely the prices of labour, equipment and materials, and ending up with mines that cost them far too much to build. They also develop lower-grade mineral deposits, the exploitation of which becomes uneconomic as soon as the world price drops back from its record heights. In the aftermath of the boom, many acquisitions are written off, the chief executives who presided over these excesses get the chop and are replaced by bosses whose main skill is cost-cutting. They make speeches about how excessive Australian wages are. Anyone who has followed the fortunes of our big three - BHP Billiton, Rio Tinto and Glencore Xstrata - will know just what I'm talking about.

In their race-driven frenzy to start new projects, the miners always portray themselves as impatient for God's will to prevail, with any politicians or community members who have doubts about allowing them to rip up the environment denounced as agents of the anti-progress devil. In the aftermath of such booms we realise we should have refused to be rushed. Why does no economist ever warn us to be less short-sighted? Their faulty model. Ross Gittins is the economics editor. Twitter @1RossGittins