Just because you understand something deeply and possess the pedagogical skills to explain it to an elderly layperson doesn't mean it's suddenly easy after you've explained it, and doesn't mean it was easy to put in the hard work required get to that level of understanding. Breaking something complicated down and explaining it to a layperson is a different thing than actually doing the work yourself.

Are you suggesting that if one is able to explain a complicated problem to their grandmother, somehow the original problem was actually easy, or is made easy by this explanation? I haven't read Einstein's book on relativity linked in your sibling comment, but I don't think the existence of this book makes relativity an easy thing to have worked on.