Tim Harford in Reason Online:
Economists used to think wealth came from a combination of man-made resources (roads, factories, telephone systems), human resources (hard work and education), and technological resources (technical know-how, or simply high-tech machinery). Obviously, poor countries grew into rich countries by investing money in physical resources and by improving human and technological resources with education and technology transfer programs.
Nothing is wrong with this picture as far as it goes. Education, factories, infrastructure, and technical know-how are indeed abundant in rich countries and lacking in poor ones. But the picture is incomplete, a puzzle with the most important piece missing.
The first clue that something is amiss with the traditional story is its implication that poor countries should have been catching up with rich ones for the last century or so—and that the farther behind they are, the faster the catch-up should be. In a country that has very little in the way of infrastructure or education, new investments have the biggest rewards.