For years passive solar design principles have been perpetuated without being reexamined or questioned regarding their relevance in the context of new materials and constructions. Rarely does an architect get quantitative feedback on system or concept performance after the building is built. The result has been the perpetuation of beliefs among conference papers, text books and popular articles, all too often based only on belief. In this paper examples of premises which likely deserve to be kept passive rather than acted on are challenged. Designers are encouraged to ask three questions when applying a commonly held rule or assumption: Does it address the right issue? Does it apply, given the properties of new components and materials? If the premise is violated, how badly is comfort or the energy balance affected? Examples taken from monitoring and sensitivity studies illustrate the importance of asking ＇＇stupid＇＇ questions.