If you can’t explain something in simple terms, you don’t understand it
This strikes me as raw arrogance. Complexity is intrinsic to many systems that are subject of expert study. To tell someone who has devoted their career to understanding a complex topic that they don't understand their subject because they can't express it in layman's terms without doing terrible violence to the underlying phenomenon is ludicrous.This is the sort of thing you'd believe if you were an arrogant 20-something who thought they could learn any subject in a few hours, cushioned thoroughly by the illusion of understanding."Oh yeah, I understand the mechanisms of human vision. It's just rods and cones.""I understand the causes of the American revolution. It was just people protecting their property.""I understand Joyce's Ulysses. It's just follows three people from Dublin over a single day. I read the Cliffs notes.""I understand why coffee makes me alert. It's just blocking some brain things that make you sleepy."Now, I will agree that if you don't know how to break interactions down into teachable parts, you will probably have trouble as an engineer or scientist both advancing your own knowledge and introducing people to the field. But to suggest that your understanding of a subject hinges on being able to deliver an explanation in simple terms is just silly.