Bryan Caplan shares the Iron Laws of Pedagogy:
First Iron Law: Students learn only a small fraction of what they’re taught.
Second Iron Law: Students remember only a small fraction of what they learn.
Third Iron Law: Most of the lessons students remember lack practical applications.
Research on Transfer of Learning strongly confirms a fourth, less obvious conclusion:
Fourth Iron Law: Even when students remember something with practical applications, they still usually fail to apply what they know… unless you explicitly tell them to do so.
Everyone knows them from firsthand experience, but no one admits them publically.