However, for Hirschman growth was always, everywhere and necessarily, an intrinsically uncertain and uneven process -marked by rapid advances in some sectors followed by catching up in others. This made the principal challenge for policymakers the search for complementarities across industries rather than scale economies. The role of the state planner is to assess w hether productive private investment or infrastructure investment will induce the most progress in other industries, through creating excess capacity or shortages. Hirschman introduced the concept of (backward and forward) linkages as the mechanism for simultaneous and progressive expansion in both domestic demand and supply and to better identify the sectors to focus on.