Was it Einstein who said, "Any scientist who cannot explain what they are doing to an eight year old is a charlatan"?
No. It's commonly attributed to Einstein, but of course he didn't say that, because he knew better. There are things you just can't explain at a certain level. For example Feynman couldn't explain to a layman how magnets work, but explained why not: https://www.youtube.com/watch?v=wMFPe-DwULM.