This is the sort of thing that's great for helping engineers go from junior to mid-level and then dangerous for going from mid to senior. Thinking clearly about exceptions to "rules" is one of the most important skills you can impart.

Don't Repeat Yourself is great advice... but only if you start thinking about all the caveats where over-application leads to architectural disasters.

The GP is largely correct here: If your advice includes "never" or "always", you're probably doing more long-term harm than good.