I explained the contrast and grain issue to my friend, which she understands and is okay with. She did take issue with how stops are "numbered," though (400 to 800 is "only" 1 stop?). She can work the numbers (shutter and aperture), but I can't explain _why_ things are numbered that way (it involves some math, which is my great failing).
Unfortunately, my explanations use bad analogies and probably makes things worse. To make a bad analogy about my analogies, it's like using cosine to explain sine - if you don't understand one, it can't be used to illustrate the other.
Shutter speed and ISO works in the same manner though, i.e. doubling the number = 1 stop. 1/500 to 1/1000 is one stop too.