He’s restating the “Johari Window”, a psychological technique for describing the gap in understanding between oneself and others. It’s taught in many management classes, including the one I attended.

https://en.m.wikipedia.org/wiki/Johari_window

By dividing knowledge into two axes, things one knows on one, and collective awareness on the other, all outcomes get covered.

It’s just a lot more of a mouthful when described instead of shown as a simple chart.

Poor Rummy, he rightly gets a lot of stick but I think he did a pretty good job of verbalizing the concept.