We're not out to get our students (Art Carden).
Property rights are probably the most important economic concept ignored by most principles courses. An interesting piece on property rights and karaoke (NPR).
Sometimes economists get principles of economics questions wrong (Tabarrok); sometimes economic researchers claiming that economists get principles of economics questions wrong write the question wrong (Cowen); sometimes there's more than one answer (Decker via Depken). Lesson: we have to be thoughtful about writing the questions we ask students.