Only the original thread that created a view hierarchy can touch its views.

This means that only the thread that created a view hierarchy (e.g. the main thread in Android) is allowed to modify or interact with the views within that hierarchy. If another thread attempts to modify a view, an exception will be thrown. This restriction is in place to ensure that views are accessed and modified in a thread-safe manner, preventing potential concurrency issues and ensuring that the user interface remains responsive and stable.