Stack Exchange explicitly encourages writing a self-answer, when appropriate.
Derek Muller posted a video about a wind-powered vehicle that can go downwind faster than that downwind itself.
(The design of the vehicle dates back multiple years, but building one that is large enough to move a human (and not kill the human by falling apart) has proved challenging, by the looks of it.)
In the video Derek himself indicated that he was not quite confident that he understood the physics of it. I anticipated that questions would start coming in on physics SE, so I posted a self-answer.
Now, this being a self-answer it felt silly to pretend (in the question) that I didn't know the answer.
Also the subject is:
'A wind-powered vehicle on wheels that can go downwind faster than the wind itself.' I assumed that any physicist would immediately go: "Hang on, how is that possible?"
The question was closed on the grounds: 'needs details or clarity'.
So I'm asking for opinion here.
It seems petty to me to close a question because the obvious isn't stated explicitly.
For the future:
Should the question part of a self-answer be phrased as if you don't know the answer?