By including immediate gratification as a main motivator for online purchases, the fast growth of e-commerce has changed consumer behavior. This review looks at the psychological processes behind impulsive buying behavior and post-purchase dissonance—two connected phenomena becoming more and more common in digital markets. Driven by dopamine release and reinforced by persuasive UX/UI design, scarcity cues, and AI-powered personalization, instant gratification promotes fast decision-making by reducing cognitive friction. These actions are amplified by social commerce, influencer marketing, and gamified shopping venues that use FOMO—fear of missing out—and social validation systems. But the very elements that promote instant purchases also cause increased post-purchase conflict, a state of regret or dissatisfaction brought on by unmet expectations. Based on Festinger's Cognitive Dissonance Theory, this review looks at personal, product-related, contextual, and technical influences that exacerbate this emotional fallout, including price sensitivity, product complexity, urgency cues, and social pressures. The study reveals how gender, cultural norms, and social support networks affect the severity of regret, therefore influencing consumer reactions including returns, complaints, and bad reviews. E-commerce systems use a dual strategy—maximizing conversions through urgency and personalization, while minimizing regret through clear return policies, proactive customer support, and loyalty programs. However, current research reveals critical gaps, including the lack of longitudinal studies on gratification–regret cycles, limited exploration of personality–technology interaction effects, insufficient understanding of emotional recovery post-return, and minimal attention to the ethics of persuasive digital design. This review provides a conceptual model for striking a balance between profit-driven urgency and consumer psychological well-being by combining ideas from behavioral economics, neuroscience, and digital marketing. The results ask e-commerce participants to implement design and policy measures that maintain consumer happiness beyond the point of sale, hence developing ethical, sustainable, and trust-based digital economy..