Here's why it's hard to pinpoint an origin:
* Common Usage: The phrase is simply a natural way to express the idea of starting or beginning something. It doesn't have a particular historical event or literary source attached to it.
* No Official Records: Language development doesn't always have official records or documentation. Phrases often evolve organically through everyday speech.
* Similar Phrases: Many similar phrases exist that convey the same meaning, like "starts at" or "commences with."
Therefore, while the exact origin of "begins at" is unclear, its use is a natural consequence of the English language's development.