The Dumb-Down Principle, which entered Dublin Core discourse in 1998, denoted a principled way of viewing a complex metadata description through the lens of a simpler representation, typically Simple Dublin Core.
Dumb-Down was relevant to the use of Qualifiers, which were seen as a way to add context to a metadata value - clarification of meaning, references to specific controlled vocabularies or parsing rules, and the like. According to the Dumb-Down Principle, it should be safe for an application to ignore a qualifier, use the value as if it were unqualified, and expect that the value, though semantically less specific, remain correct and useful. For example, an "alternative" title is valid and can be useful as a title in the absence of knowing that the title is "alternative".
This notion of Dumb-Down faded as the Dublin Core community shifted to an RDF-based interpretation of qualifiers, such that
http://purl.org/dc/terms/alternative, for example, actually meant "alternative title" and not just "alternative" (despite the awkward lack of "title" in its URI). Such a sub-property could be resolved to its better-known superproperty,
http://purl.org/dc/terms/title (in the spirit of Dumb-Down), but it could not simply be ignored. As this interpretation became the basis for DCMI Metadata Terms and the DCMI Abstract Model, the Dumb-Down Principle, in its original meaning, faded in relevance.