Rich countries make rich-country things. Poor countries make poor-country things. According to the theorem of comparative advantage, you should specialize in whatever you have relatively low costs - but we also know that over time, countries grow rich by changing and upgrading what they produce.
But why have some developing countries grown into diversified, mature economies whereas much of Africa is still stuck growing or mining a few basic commodities?
This answer comes from Cesar Hidalgo, Bailey Klinger, Laszlo Barabasi and Ricardo Hausmann, who just got it published in Science (or see here for the full version):This diagram shows the 'product space'. Imagine international trade as a forest, with individual products making up the trees. Firms are like monkeys swinging through the trees. The closer the trees are together, the easier it is for firms to move from one tree to another. Thus firms and countries specializing in products in ‘denser’ areas of the forest can diversify more easily. Countries tend to move into the centre over the time - but the denser the part of the forest where they start, the quicker they will get there.
Where does Liberia fit within this product space? It turns out that most of Liberia’s exports are within the sparsest part of the forest: rubber, cocoa, iron ore and palm oil all have extremely poor links to other products. See where tropical agriculture is in the diagram above . . . and compare it with garments, say, or vehicles and machinery.
The implication of this is that export diversification will not be easy in Liberia, because the economy has specialized in products that are very remote from other products. It takes 7 years for a rubber or cocoa tree to become economically useful. Rubber or cocoa plantations are therefore a huge ‘sunk cost’ and difficult to change. On the other hand, neighbouring countries like Ghana and Nigeria show the perils of trying to develop industries in which you don't have a comparative advantage. Maybe fruit, vegetables and low-tech food processing (canning, juicing) are a way forward.
If you go to the authors' website, you can download the map and the data for your country. A blinding insight or another example of economists restating the obvious in a more complicated way?