Do you have a convincing explanation, or just one based on the limits?
Well, the one I gave has convinced every student I've ever used it on, although it's more convincing when backed up by the proper diagrams.
I am a great believer in the KISS principle and avoid getting into mathematical explanations whenever possible, particularly when the student may not even have passed maths at GCSE. Clearly, that is not always possible but in this case, it is.
As for terms like circularity and locussszzzzzzzzzzz!