Modern UI architecture is evolving from the traditional separation of frontend and backend development towards a composition-based approach that prioritizes the user experience. Historically, developers have divided responsibilities between frontend interfaces and backend logic, with APIs serving as intermediaries. However, with the rise of single-page applications and component-driven frameworks like React, there has been a shift towards making each UI component self-sufficient, capable of handling its own data needs without relying heavily on generic backend endpoints. This approach, known as Backend for Frontend (BFF), aims to streamline data fetching by tailoring responses to specific UI requirements, reducing the need for multiple requests and extensive client-side logic. React Server Components further this paradigm by allowing components to fetch data independently, promoting colocation of data-fetching logic with the component itself. This shift encourages developers to think vertically—focusing on UI units like posts and buttons—rather than horizontally across technical layers. By adopting a composition mindset, developers can create more maintainable, reusable, and user-focused applications, aligning the architecture with how users perceive and interact with the interface.