[Double Naught Spy]

What Mr. Borland is talking about is a condition referred to both as "inattentional blindness" or sometimes "attention blindness." You are blind to something you can physically seen because you aren't paying attention to it or your are blind to an object you can physically see because you are paying so much attention to something else - different perspectives on the same situation.

Basically, you brain has only so much computing power and you cannot comprehend all items in your field of view to the point necessary to understand how each and every one of them can be applied to your immediage situation, especially if it is an immediate situation for which you are not prepared or in which you are not experienced.

Case and point, people will often run to a fire exit they see when they realize a fire has broken out even if it is a distant fire exit, much further than one they just passed. They might have seen the one they just passed, but because of their attention being elsewhere, the information was not filed, categorized, and organized as being immediately relevant and was summarily overlooked when the crisis occurred. This was a particular problem on airplanes where passengers tended to go to the exits in front of them (when seated) and not to much closer exits behind them (that they saw when boarding) and hence why part of the program on planes is to make passengers aware of all the relevant exits and that the closest exits may be behind the passenger.

Of course, the blindness isn't just about sight. It may well affect hearing, smelling, tasting, and feeling, though humans tend to glean most of their information about their environment visually.