This paper presents Systematic Theory Mapping (STM), a comprehensive and systematic method, as the first step toward defining and dealing with complex and wicked problems. Social systems exhibit a messy, multifaceted, and multi-level composite of problems characterized by causal complexities and non-linear interactions of numerous contributing variables. Exploring such a wicked composite of problems for causal explanations and theory building through reductionist empiricism is unrealistic, expensive, and futile. Systems thinking is required to understand the configurations driving wicked problems and navigate their causal complexities. We construed brand externalities as a wicked problem and provided an illustrative example for STM. A systematic narrative review is used to amalgamate diverse stakeholder perspectives and capture the structures and processes that generate brand externalities. System dynamics, employing a causal loop diagram, is used to organize the findings and develop a causal theory of brand externalities. The proposed method can help scholars, managers, and policymakers better define complex managerial and social problems and identify the likely consequences of their actions.