Feynman, I guess because he interacted a lot with laymen (an lay-women) knew that the knowledge frame of the audience is very important. If you think this is obvious, wait till you try to explain internet addresses, cloud storage, etc. to your mom (or grandma), or as in the well-known case (http://tomayko.com/writings/rest-to-my-wife) the REST protocol to your wife.
It's very hard to estimate the level of explanation that will actually convey information to the person asking teh question while at the same time keeping them interested.
It all gets summed up in the last sentence, which is really a killer:
> But I really can't do a good job, any job, of explaining magnetic force in terms of something else you're more familiar with, because I don't understand it in terms of anything else that you're more familiar with
I've never heard that impedance mismatch being told in such clear, humble words. Basically, he's saying "I know things in so much detail that I can't in all honesty imagine wrongful analogies, let alone present them to you".
He's not saying that he "knows things in so much detail that he can't imagine wrongful analogies". He's saying that "magnetic force is different from anything you are familiar with", so you have to learn it as something new, not by analogy.
Feynman does (explain a little bit of) Quantum Mechanics by analogy (photons are spinning clocks), but goes on the say you have to learn a truly ne wmodel to understand more deeply.
> It is the most common way of trying to cope with novelty: by means of metaphors and analogies we try to link the new to the old, the novel to the familiar. Under sufficiently slow and gradual change, it works reasonably well; in the case of a sharp discontinuity, however, the method breaks down: though we may glorify it with the name "common sense", our past experience is no longer relevant, the analogies become too shallow, and the metaphors become more misleading than illuminating.
There are lots of gems in that essay, such as this:
> We can view the program as what turns the general-purpose computer into a special-purpose symbol manipulator, and does so without the need to change a single wire (This was an enormous improvement over machines with problem-dependent wiring panels.) I prefer to describe it the other way round: the program is an abstract symbol manipulator, which can be turned into a concrete one by supplying a computer to it. After all, it is no longer the purpose of programs to instruct our machines; these days, it is the purpose of machines to execute our programs.
It's very hard to estimate the level of explanation that will actually convey information to the person asking teh question while at the same time keeping them interested.