I think if you understand something really well (anything: the law of gravity, the Curry-Howard isomorphism, electrolytic dissociation, general relativity,...), you can find a bunch of comparisons, or metaphors, or other ways to explain it so that an interested five-years-old will get a rough idea. A very rough idea indeed, but one that could allow them to ask qualitatively reasonable questions, and that forms an intuition which helps during a real study.

The "interested" part does a lot of lifting though. It's really hard to explain things to uninterested people.

If the person you are explaining your project to is not interested in the technical side, presumably under the rather confused but popular theory that technical aspects are not relevant to technology ventures, you'll not be making headway. It's much better to just make up some dollar numbers and run with that.

I would say: You either don't understand your subject, or don't understand your audience, if you can't explain your subject to your audience, at the highest level they can understand, coherently.

The average person can understand anything ... at some level. Being able to match that level is positive evidence (but not proof) of competence.

Duality: Being unable to match that level is positive evidence (but not proof) of incompetence.

I suspect Feynman actually haven't been to the world of the middle-to-bottom sections of the bell curve, where that thinking becomes toxic. It only works because there's collective illusion that minority theorizations can be more correct. Absent that, or that inverted, majority becoming assumed likely more correct, not only one's explanations will be interpreted biased as likely more wrong, but acts leading to majority groups following your round-Earth hypothesis can be seen as manipulative and/or fraudulent. That kind of people(which exist) abusing versions of those lines get annoying fast.