When React launched in 2013, its defining idea was strict one-way data flow: parents pass data down via props, and updates happen in a clear, explicit place. Children can't mutate parent state directly; they signal changes through callbacks. The result is predictable, traceable state changes.

This contrasted with MVVM frameworks like early AngularJS, Knockout, and WPF, which relied on two-way data binding. That automatic syncing felt convenient for small apps, but at scale it often led to hidden coupling and hard-to-trace update chains.

Over time, many developers came to view pervasive two-way binding as a design mistake in complex systems. React's unidirectional model gained traction because it favored clarity and control over "magic."