"Focusing", when used about mental attention, is a metaphor, taken from the way lenses work.
Camera lenses are "out of focus" only in the context of something you want to photograph. Lenses always focused on some spot in space. There may not be anything at that spot. But if you put something there, that's what the camera is focused on.
But what would "blank out" refer to in regards to a camera? I guess to the shutting of the aperture. The apparent correspondence, as regards mental attention, is becoming unconscious. This isn't something you have direct control over, as many an insomniac has learned.
I think that when people refuse to attend to an unwelcome fact, they don't do it by truly shutting down their consciousness. Rather, they do it by shifting their consciousness to something more immediately acceptable.
If you're telling somebody something unpleasant,
and they cover their ears and chant "Om",
in fact they're aware that you are still present
they're just hoping that you will go home.