In his article "Principled Practical Knowledge: Not a Bridge but a Ladder," Carl Bereiter (2014) argues that theoretical knowledge is too shallow to support the generation of innovative learning activities. He makes a case for principled practical knowledge (PPK)--"principled know-how and know-why"--to fulfill this practical generative role. We argue and illustrate in this commentary that PPK as portrayed by Bereiter does not offer much practical guidance for 2 potential users: professional designers and teachers. For professional designers PPK should be further specified in order to fulfill its generative role. But even this enriched form of PPK still does not suffice to address the challenging issues of practicality teachers face. We explain the magnitude and dimensions that underlie practicality in the everyday work of teachers and suggest how recent work on fast and frugal heuristics can contribute to helping teachers to make instructional innovations practical.