Using one field and two online lab experiments, this article shows that congruency between shelf layout and a consumer’s internal product categorization increases the perceived variety of the assortment and reduces the perceived complexity of the shelf layout. These assortment perceptions, in turn, heighten purchase intention and satisfaction toward the chosen item. Results are robust across internal categorization measurements (planogram design vs. sorting tasks), congruency measures (distance- vs. matching-based), and products (biscuits vs. yogurt snacks). In the field study, familiarity—operationalized as either consumption frequency or subjective product knowledge—increased the overall effect of categorization congruency and strengthened its pathway through perceived variety (vs. the one through complexity). The authors show how their research can be exploited to improve shelf layouts by optimizing the external categorization. They demonstrate the value of a unifying Bayesian framework for research on behavioral decision making that uses the same set of posterior parameter draws for parameter inference, moderated mediation analysis, and optimization under uncertainty.