If you are a true master, you should be able to explain concepts in a way that even a child can understand
This is, in a word, horse pucky. It's the same reasoning my niece uses to justify her anti-vaxxer beliefs: the quacks and charlatans she listens to are more credible than epidemiologists and immunologists because they're easier to understand. This is the real-life equivalent of the joke about searching for the $20 bill under the street light because where you actually lost it is inconveniently dark.
If it were true that a child could understand anything, there wouldn't be a need for education. You'd just find a "true expert" to explain, say, fluid dynamics to a random bunch of people off the street and then set those randos to work designing aircraft. Or cryptographic systems.
There's an unfortunate cultural trend to devalue anything that requires mental effort and dedication to understand as elitist bullshit. This is a dangerous development, especially when combined with our national vanity: ever since the Moon landing we see technological and scientific leadership as a birthright. It's not. It's something we have to earn, and continue earning every day by dint of hard labor.
The humbling truth is that real understanding in many things requires trekking a long and arduous road. It's a near certainty that you don't actually understand General Relativity; crude analogies about balls and rubber sheets notwithstanding. General Relativity is like a mountain that looks easy to tackle from a great distance, but the fact is it takes years of toil before you can even grasp how arduous the foothills of Mount Einstein are.