Such “ranked equilibrium” reply on the presence of a complementarity: a particular form of externality in which the taking of an action by an agent increases the marginal benefit to other agents from taking the similar action. In the argument above, sector-specific investments lie at the heart of the complementarity: more investment in one sector raises the return to investment in some related sector. Once complementarities — and their implications for equilibrium multiplicity — enter our way of thinking, they seem to pop up everywhere.