While it may have sounded somewhat awkward to laymen (for whom it was actually intended), it was an attempt to lay out a basic grid for threat assessment. Unknown unknowns would be a Black Swan event.
No way to prepare, no way of really even knowing what hit you until you're well into the event or problem. Blindsided by something you couldn't even envision prior, more or less.
Yes...the Black Swan. Gotta hand it to the person who coined that phrase. Perfect.