How many times have you read an essay and thought to yourself: why hasn't the author considered this or that? When authors write, they have an thesis, objective, or aim in mind. Sometimes it is to persuade a reader to take up a position. Sometimes it is to report a happening. Sometimes, such as in philosophy, it is to argue for a specific conclusion. Regardless of what the author intends to do, they have evidence or use assumptions that draw the reader's attention toward that conclusion or thesis. In taking up these different forms of evidence, they set aside other pieces of evidence or different assumptions either because they fail to adequately support the conclusion the author's trying to reach or they think the evidence is superfluous. It is not necessary to draw the reader to the appropriate conclusion.
The aim or objective usually, but surprisingly, takes one's attention away from an obvious point that the author may have thought of if they weren't so focused upon their own aims.
Call this phenomenon a thinking blindspot. A thinking blindspot is a lot like a blindspot in one's rearview mirror when driving a car. The driver isn't aware of the blindspot until someone points out that the driver cannot see something that occupies the space beside the vehicle. Blind spots also may limit our problem-solving skills and hack away at our creativity.
The author may not even become aware of the oversight until after the article or report is written and someone points out the blindspot to them. When they were writing the piece, they may have thought about the blindspot in passing. But, for whatever reason, the author didn't give it much more thought than that.
A blindspot is by definition something which someone is not aware of until such time as it is pointed out to them that they have overlooked whatever it is they overlooked. There are many examples of this occurring in making groundbreaking discoveries. For example, the Nobel prize winner, Carleton Gajdusek, initially failed to see possible causes of kuru. It was only years later that he realised what the cause of the dreaded disease was.
Thinking blindspots come are various. For example:
Not stopping to consider something that looks unconnected
Jumping to conclusions based upon shoddy evidence
Getting trapped by categories commonly upheld by peers
If we have thinking blindspots, then could this at least partly contribute to an explanation for why we are so bad at selection tasks? We are bad reasoners because we fill-in data. Or we are bad reasoners because overlook some important piece of information. We overlook it because we don't believe it is important. Think here of Wason's selection task. The study participant is less likely to turn over the card that would reveal whether the conclusion follows because they're distracted by the other card that seems so much more obvious the one to choose to turn over.
Perhaps better, more acute rational thinkers, i.e., those thinkers who are less apt to miss something in their thinking, have a greater capacity for being aware of something in their blindspots. Moreover, they are likely not to become distracted by details. Those who are more susceptible to blindspots become easily distracted by other things or are more apt to overlook something.