The Architecture of the "Buy" Button: Digital Nudging, Gamification, and Retail Investor Behavior in Zero-Commission Brokerages

AbstractThe democratization of retail investing over the past decade has coincided with a fundamental paradigm shift in brokerage user interface (UI) and user experience (UX) design. Modern fintech platforms have transitioned away from the high-friction, analytical interfaces characteristic of legacy brokerage firms toward gamified, low-friction mobile applications. This paper investigates the behavioral and structural mechanisms through which modern digital choice architecture influences retail investor decision-making. Drawing upon Richard Thaler and Cass Sunstein’s Choice Architecture framework, B.F. Skinner’s operant conditioning paradigms (specifically variable ratio reinforcement schedules), and recent empirical asset-pricing literature, we analyze how features such as zero-friction execution, visual chromatic heuristics (red/green bipolarity), and reward feedback loops alter risk preferences. Furthermore, we examine the structural alignment between gamified UI design and the Payment for Order Flow (PFOF) revenue model, demonstrating that platform profitability is structurally dependent on trading volume rather than investor returns. Finally, we propose cognitive and policy-level interventions designed to reintroduce constructive friction into digital investment environments.