I often tell my students at Dartmouth, that if you can't explain a technical phenomenon to your grandmother, you don't really understand it.
So in teaching design of experiments, statistics, materials science, and manufacturing processes, I try to keep the Grandmother conjecture in mind.
One of my hobbies is the theory of relativity. Related to this theory is an interesting "puzzle" called the "twin paradox."
I have tried to explain it for Scientific American readers in this article. Go there to see if you think I was successful considering the Grandmother conjecture.
Note: Recently I changed the conjecture to "The Grandparent Conjecture," in deference to one of the outstanding Dartmouth female engineers who suggested this better title.