In the novel, Mentat candidates, selected by breeding and subjected to a rigorous gauntlet of intellectual exercises since birth, are trained to absorb staggering amounts of data and disparate information to sift and coalesce the relevant into concise, usable analysis. Most children who undergo this intense process fail out before adolescence; fully-trained Mentats are considered supreme logicians and highly sought after across the Imerpium as advisors to ruling royalty, military leaders and guild directors.
A significant element of Mentat training was their efforts to cultivate what was called 'The Naive Mind' - to see things as if for the first time, ridding oneself of preconceptions and prejudice that mar most human's capacity for objectivity.
Cognitive psychologists are long familiar with the phenomenon of Confirmation Bias - the natural tendency for people to seek out and overcount evidence that supports our beliefs and dismiss data points contradictory to our world view. Once we arrive at a conclusion about something - human nature is loathe to revise our beliefs and often dig in our heels to avoid the emotionally unpleasant experience of admitting we were wrong; our egos freezes our ability to objectively sort new information that may challenge our existing assumptions, limiting our ability to grow and evolve intellectually.
"Chunking" (Cognitive Psychology)
Some may be familiar with the psychological term 'chunking;' as adults, we 'chunk' previously small bits of data into compressed macro-units so we can process larger amounts of information more effectively. Using the computer an analogy, humans have a finite amount of RAM that cannot be upgraded - the standard way to process more information is to compress data into that finite space through mental shortcuts and cognitive 'chunks.'
Those of you who play musical instruments know this intuitively; when you first learned an instrument, notes are learned one by one ... strung together clumsily and with great difficulty. As time passes, your mind aggregates certain strings of keystrokes/motions into mental 'chunks' which become your new the 'unit' of thought, until entire concertos become a single fluid stream of memorized motions that flows from your fingertips to the audience. Most of us have experienced the phenomenon where a music teacher asked "now please start from the first four notes from the third measure," only to draw a blank - we know songs from certain anchor points but we reached a level of musical proficiency in which such requests are at a level of granularity below our ability to process.
(More on the topic can be found by reading the Wikipedia entry on Chunking)
The Naive Mind and Confirmation Bias
We've all seen examples of Confirmation Bias in the people around us - political partisans (Democrat or Republican) who believe members of their own party can do no wrong, and gleefully trumpet the misdeeds of their enemies as proof of their own moral superiority. Religious zealots who seize upon an ambiguous fossil discovery as 'proof' the Earth is as Biblically-stated, only 5000 years old.
More prosaically, we carry private biases about people in our lives - some well-deserved, others perhaps not so - which limits our relationships with them.
The discipline of cultivating "the Naive Mind" is being able to retain the ability to zoom in and zoom out of cognitive granularity at will - to see things as a seasoned expert and then see that same thing again piece-by-piece as if for the first time.
So what does this mean in practical terms?
In my life - I found it helpful to articulate my assumptions: the things I believe, the things I *want* to believe to be true.
Knowing human nature and its tendency toward Confirmation Bias, I make a deliberate effort to view evidence that supports those things I believe with heightened skepticism as a way to offset my natural biases toward wishful thinking; at the same time, I give a measure extra credence and credulity to things I normally disbelieve/disparage. Divorcing my ego from my beliefs is a continuous process, but in so doing, it helps to ensure that - like in My Favorite Liar, beliefs are constantly evaluated against facts, and capable of withstanding logical challenges.
And while I may never ascend to be a Mentat-Duke or lead humanity on the Golden Path, it's the best we can manage without a ready supply of Spice and a Barony at my command.