When and why it was written

When

Around 170 CE, in the last book of the notebooks.

Why

Written by a man with more latitude than anyone in the empire, and therefore in need of a rule that ignores latitude.

What it means

The structure is two tests, each requiring one decision and no deliberation.

Its value is that it forecloses the negotiation. Most wrong acts are not chosen against a clear rule; they arrive after a stretch of reasoning about why this case is different. A test this short leaves nowhere for that reasoning to happen.