You don’t understand something until you can explain it simply.
Not simplified. Actually simple. Without jargon masking a gap in understanding.
Feynman built his method on this. The physicists who couldn’t explain quantum mechanics in plain language didn’t have a communication problem. They had an understanding problem.
I’ve seen it most clearly in risk reviews. Two people in the same room, looking at the same data. One produces three pages of framework. The other says: what’s likely, what it costs, how to reduce it. The second person understood the problem. The first had borrowed the vocabulary without building the model.
The rarest skill isn’t knowing more. It’s knowing enough to make it disappear.