Between $6 and $9 trillion dollars—about 8% of annual world-wide economic production—is currently being spent on projects that individually cost more than $1 billion. These mega-projects (including everything from buildings to transportation systems to digital infrastructure) represent the biggest investment boom in human history, and a lot of that money will be wasted.

Just seven recent mega-projects total up to almost the entire debt between the world’s two largest economies.

Humans have always wanted to build big, whatever the consequences. Even the earliest religious mythology refers to attempts to build a tower to the heavens, often ending in disaster. And early civilizations around the world undertook giant constructions such as the Taj Mahal in India or the pyramids in Egypt at great human cost. And yet we keep doing it, and the reason has to do with our willingness to fool ourselves.In the late nineties, Bent Flyvjberg, now an economist at Oxford University’s Said School of Business, watched his home country of Denmark building what was the world’s longest suspension bridge and second-largest undersea tunnel. The project was a disaster of biblical proportions, Flyvjberg says, with problems ranging from cost overruns to floods and fires, and the taxpayers were taking a loss before it was even finished. But there had been no comprehensive study of whether these problems were were typical of such projects, so Flyvjberg set out to find out the answer.

…. more independent analyses of existing proposals, as well as efforts to recognize the incentives for bad forecasting that come with the financial and political interests of those touting the projects.One promising sign he sees: Mega-projects are more and more likely to damage people’s careers, especially as they move into the digital realm. Cost overruns with the Airbus A380 jumbo jet cost a chief executive his job; a failed IT upgrade at K-Mart lead to the company’s bankruptcy, and China’s rail minister lost his job over corruption and safety problems. Even US president Barack Obama’s reputation has been dented by the troubled rollout of digital marketplaces built as part of his signature healthcare reform law.

“IT projects are like ticking time bombs, and they can undo people’s careers, whole companies and now even presidencies,” Flyvbjerg told Quartz. “We find it a fascinating area to study.”