A framework for improving decision-making in complex adaptive systems like business and investing. Mauboussin argues that success in environments defined by complexity and uncertainty requires moving beyond first-level thinking. He explains how recognizing biases, challenging mental models, applying the “outside view,” and distinguishing skill from luck can strengthen judgment. By using structured tools—such as checklists, decision journals, and premortems—and focusing on the quality of the decision process, leaders can reduce costly errors and make more consistently sound decisions.