Scratch any global mining or oil company and you might find a fear that dare not speak its name.
That name is resources nationalism, an issue becoming increasingly acute as countries militate against foreign resource extractors operating on their land.
The problem is success. The more successful the extractor, the more demanding governments and their associated stakeholders become. Studies show that as a commodity's value rises, so does the legal and political action against its extractor.
Examples, particularly in Africa, are surfacing more regularly. In March the UK-based and listed African Consolidated Resources (ACR) had its licence to mine Zimbabwe's Marange diamond fields cancelled by the government after a protracted legal process.
The company won its initial High Court appeal, but the Zimbabwe government invoked new grounds for cancellation based on other laws.
Robert Mugabe, the president, and his Zanu-PF party have since demanded that the government be given a majority stake in any foreign miner extracting Zimbabwean minerals.
ACR is not alone. Namibia is a more recent cause for concern for Australian miners there as the government has declared uranium, copper, gold, zinc and coal to be "strategic" minerals.
Namibia wants the state-owned mining company, Epangelo, to hold exclusive exploration and mining rights to all of these commodities.
At a conference in Hong Kong in March, Rio Tinto's chief executive, Tom Albanese, invoked "the curse of resource nationalism", which he says has become a major obstacle to mining projects as governments and their associated stakeholders demand a bigger share of the profits from important commodities.
Mr Albanese, who runs the world's second-biggest mining company, said "human constraints" were becoming the most difficult issues.
While he did not exactly enunciate what these human constraints were, miners fear the kind of attitude advanced by Bolivia, which has refused foreign access to the country's lithium deposits.
"We will not repeat the historical experience since the 15th century - raw materials exported for the industrialisation of the West, which has left us poor," said the Bolivian mining minister, Luis Alberto Echazu. No doubt African countries that are enjoying mineral booms are flexing their muscles, but it is not just about a big western company exploiting the wealth of a poorer nation.
In an obvious reference to Australia itself, Mr Albanese said that in countries "with good governance and infrastructure" there was a pattern of "increased activism of stakeholder engagement".
Australia's proposed resource super profits tax, designed to give more mineral wealth back to the people, has been a worry for all local miners. Rio itself, with help from BHP Billiton and Xstrata, successfully lobbied to water down the tax.
Canada has also shown reluctance to allow in foreigners, recently killing off BHP's US$39 billion (Dh143.24bn) bid for the fertiliser maker Potash.
Miners fear that whenever there are larger profits and margins over a sustained period, the pressures for higher taxes and royalties increase. Sometimes, governments take a stake in the resource after the investment has been made, causing greater investment uncertainty.
Mr Albanese's fears do not appear to be unfounded. The Russian academics Sergei Guriev, Anton Kolotilin and Konstantin Sonin jointly studied the movement of oil prices with oil asset expropriations and concluded that expropriations always occurred in periods of demand.
The authors looked back to mid-2007, when ExxonMobil and ConocoPhillips, both major US-based oil companies, were forced to abandon their multibillion-dollar investments in Venezuela.
Other multinationals, while not leaving, had to concede their controlling interests. TNK-BP, BP's joint venture in Russia, had to sell a major stake in its oil business to the Russian gas monopoly Gazprom.
Earlier, Royal Dutch Shell sold a 50 per cent plus-one-share stake in the Sakhalin-2oilfield to Gazprom after it was threatened with a licence withdrawal.
Could the same apply to coal, iron ore, uranium and copper?
Past experience suggests the risk is there for those operating in territories where governments are regarded as less accountable.
Mining companies need to be aware that a rich vein of resources may look like El Dorado, but even El Dorado can came with "human constraints" attached.