Physics education researchers often design activities, then test whether the activities are effective in helping students learn. Many published activities have been described in the physics education literature. However, some instructors may want to create their own activities; these instructors may want to know about how the published activities were designed. To this end, we have interviewed several prominent designers and analyzed their publications as well as an American Association of Physics Teachers' report on lab design. This paper focuses on a particular set of design philosophies that were important to these designers. "Revisiting cycles," which address a single question in depth, were a common theme. We also argue that designers' view of conceptual learning and of "thinking like a physicist" shapes their design plans.