Find the counterexample

Here is a rule I have been working from: {{rule}}

Find the cases where it fails. Real ones, described concretely enough that I could
check them — not "it depends on context".

Then say whether the rule is still worth keeping with an exception attached, or
whether the counterexamples are common enough that the rule should go.

What to fill in

{{rule}}

The rule or heuristic — e.g. prompts with more than three blanks never get used