I was commenting on a recent training workshop (systems thinking for medical school deans. No, I'm not one), and my point was that the expert running the session had done such a smooth job that it felt like he hadn't taught us anything, but had felt instead as if we'd been talking about ideas we all knew well and were part of our everyday internal dialog.
It struck me that it's the same sensation as when you hear a new song that feels like you've known it forever. Or see a movie, artwork, etc., that already seems like it's yours.
When it's done just that well the audience doesn't have to get comfortable with it, they're already comfortable.
With good design (good teaching, good art) the audience feels like the material has always been a part of their world.