Influential theories claim that institutions shape actor behavior but are sustained by these actors’ behavior. How do scholars escape from this trap of endogeneity? This article highlights a partially exogenous factor: institutional models and blueprints. Since these ideational schemes do not emerge from actor preferences, they play an independent, irreducible role in institutional creation. In fact, Latin America has borrowed many blueprints from the “First World.” But transferred to a different setting, these imported models often fail to command firm, reliable compliance and do not operate well. Therefore, informal mechanisms arise and guide behavior. External borrowing thus produces persistent disjunctures in institutional development.