In the field of Business Administration, Management and Corporate Governance, perceived security risks and technological complexity restrict retail participation in decentralized financial architectures. This empirical investigation systematically examines Adoption Determinants of Decentralized Finance (DeFi) Protocols among Retail Investors: An Extended UTAUT Model through a multi-stage experimental methodology and rigorous quantitative analytical framework. Utilizing extended UTAUT model incorporating smart contract risk and institutional trust evaluated across 512 retail fintech investors, data were gathered across multiple operational cycles and validated against established international benchmarks. The statistical and computational results reveal that performance expectancy and platform trust were primary adoption drivers, whereas smart contract vulnerability concerns significantly dampened protocol engagement. Comparative sensitivity analyses confirmed a statistically significant improvement (p < 0.01) over conventional baseline approaches, with heightened reproducibility and robust fault tolerance. These comprehensive findings provide actionable theoretical insights and practical implementation guidelines for fintech entrepreneurs, digital banking executives, and securities regulatory authorities. Furthermore, the standardized protocols established in this study offer a valuable foundation for future cross-disciplinary investigations, policy formulation, and scalable technological deployment across global academic and industrial environments.