Developments hailed as revolutionary breakthroughs in science and medicine regularly fail to realize their original promise. In this Latest Thinking video Alfred Freeborn examines a range of historical sources to analyze the insights that the history of schizophrenia can provide into this phenomenon. Freeborn recounts the emergence of a theory in the 1970s and 1980s which associated schizophrenia with larger lateral cerebral ventricles in the brain. Conveniently, these were easily observable with the new technology of CAT scanning. Widely reported as a revolutionary development, Freeborn shows that the theory was not new and of questionable merit. The case demonstrates how an externalist explanation for scientific change (giving priority to social and economic insight) is often more persuasive than an internalist one (prioritizing new theories, methods, and techniques).