The primary purpose of user interface (UI) design principles is to enhance the interaction between users and digital products. By applying these principles, designers focus on creating intuitive, effective, and visually pleasing interfaces. Key aspects like usability, accessibility, and consistency are prioritized to ensure users can navigate applications and websites seamlessly. Effective UI design not only improves user satisfaction but also boosts overall product performance. Additionally, good UI can drive higher conversion rates and foster brand loyalty, emphasizing its vital role in product development.