“Not-knowing” is emphasized in Zen practice, where it is sometimes called “beginner’s mind.” An expert may know a subject deeply, yet be blinded to new possibilities by his or her preconceived ideas. In contrast, a beginner may see with fresh, unbiased eyes. The practice of beginner’s mind is to cultivate an ability to meet life without preconceived ideas, interpretations, or judgments.
    A simple but profound way to practice not-knowing is to add “I don’t know” to every thought. This is most effective in meditation when the mind has quieted down. So, for example, if the judgment arises, “This is a good meditation session” or “this is a bad meditation session,” respond with “I don’t know.” Follow the thought “I can’t manage this,” “I need…,” or “I am…” with “I don’t know.” Like the bumper sticker that says “Question authority,” the phrase “I don’t know” questions the authority of everything we think.
    Repeating the words “I don’t know” allows us to question tightly-held ideas. Done thoroughly, “I don’t know” can pull the rug out from under our most cherished beliefs. All too often we don’t question our beliefs. And, since virtually every train of thought has some implicit belief, when we question our thoughts, we question these beliefs.
    “Don’t know” can also be directed at motivations that lead us to act. Before adjusting your posture in meditation or quitting walking meditation early, notice what belief is operating in the motivation. Then direct “don’t know” to that belief and see what happens.
    One Zen story proclaims, “Not knowing is most intimate.” I understand this to mean that what is most essential is not understood through the filter of our judgments, past knowledge, or memories. When not-knowing helps these to drop away, the result can be a greater immediacy - what some might call being intimate.
    The practice of not-knowing needs to be distinguished from confusion and debilitating doubt. Confusion is not a virtue: the confused person is somewhat lost and removed from life. With doubt, the mind is agitated or contracted with hesitation and indecision. These mind states tend to obscure rather than clarify. Furthermore, confusion and doubt are generally involuntary. Not-knowing, as a practice, is a choice meant to bring greater peace.
    But lest we take the not-knowing practice too far, Suzuki Roshi said, “Not-knowing does not mean you don’t know.” It doesn’t require us to forget everything we have known or to suspend all interpretations of a situation. Not-knowing means not being limited by what we know, holding what we know lightly so that we are ready for it to be different. Maybe things are this way. But maybe they are not.
    As a Buddhist practice, not-knowing leads to more than an intimacy and open mind. It can be used as a sword to cut through all the ways that the mind clings. If we can wield this sword until the mind lets go of itself and finally knows ultimate freedom, then not-knowing has served its ultimate purpose.
           - from Not-Knowing by Gil Fronsdal

    To be free of all authority, of your own and that of another, is to die to everything of yesterday, so that your mind is always fresh, always young, innocent, full of vigor and passion. It is only in that state that one learns and observes. And for this a great deal of awareness is required, actual awareness of what is going on inside yourself without correcting it or telling it what it should or should not be, because the moment you correct it you have established another authority, a censor.
    So now we are going to investigate ourselves together - not one person explaining while you read, agreeing or disagreeing with him as you follow the words on the page, but taking a journey together, a journey of discovery into the most secret corners of our minds. And to take such a journey we must travel light; we cannot be burdened with opinions, prejudices, and conclusions. Forget all you know about yourself. We are going to start as if we knew nothing.
           - from Freedom from the Known by J. Krishnamurti

     In 2002, when asked about the connection between Al Qaeda, Iraq, and Weapons of Mass Destruction, Secretary of Defense Donald Rumsfeld famously said:

     There are known knowns; things we know that we know.
     There are known unknowns; things that we now know we don't know.
     But there are also unknown unknowns; things we do not know we don't know.

     This was a maddening non-answer to the question, but it points to just how complex “knowing” and “not-knowing” are. In fact, it’s even more complex than Rumsfeld indicated. What about the things that we “know”, but which are actually false? And what about the “unknown knowns”, things for which we know but can’t describe how we know (e.g., the body memory of how to ride a bike, “gut” feeling that later turns out to be correct that something is “out” but you can’t articulate what)?
     And what about the “unknown knowns”, things we don’t know that we do know? At first, this sounds nonsensical, but aren’t there times when we “know” something without knowing how we know? Malcolm Gladwell’s book, Blink, is based on this premise, and neuroscientist Antonio Demasio demonstrates, in the laboratory, that we can literally “know” something before we know we know it. Demasio’s 1997 research, known in psychology circles as the “Iowa Gambling Task”, had subjects play a game in which they chose cards from one of four decks. Each turn of a card indicated how much play money they won or lost. Two of the decks would, over time, yield a positive “bank balance” and the two others, a negative one. After about 50 cards, the average subject could tell you which of the four decks were the “good” ones, and after about 80 cards, they could articulate why, but after only 10 cards, subjects would begin choosing more often from the “good” decks, but a full 40 cards before they were even aware they were doing this. When asked, they would say they were still making random choices. Their body seemed to know, though, because after those first 10 cards, a distinct physiological response (galvanic skin response) could be detected whenever their hand reached toward a “bad” deck. This is laboratory proof that our body sometimes knows and acts on information that we aren’t consciously aware of, that we sometimes “know” things that we don’t even know we know. This is, of course, how conditioning works, and it is interesting to ponder how many things we may “know” but don’t know we know, in a negative sense. For instance, the person who insists he is not prejudiced, and may even believe he is not prejudiced, but his speech and actions indicate otherwise.
     In our culture, there’s a premium on “knowing”. We reward the student who quickly responds with the correct answer and not the ones who are slow to answer because they are considering the nuances of the question. We pay stockbrokers and salesmen well if they can speak authoritatively and convincingly enough to make a sale. We are attracted to doctors who speak confidently, even though there is evidence that the most confident doctors are less effective than those who are not always so sure. It’s difficult to win an argument with someone who believes strongly in something, because a strong belief leads to what psychologists call “confirmation bias”, sifting through evidence and experience for examples that confirm our belief, a form of blindness so pernicious that we typically don’t even know we are doing it.
     There is a great bumper sticker that says: “Don’t believe everything you think”, but this is exactly what we do. We think something, and, most often, because we think it, we “know” it to be true, and therefore we don’t even have to test it. I had a teacher who liked to say that we should have a sign on our foreheads that says “Construction Zone”, because, she says, we are busy creating the reality that we believe in, but we are usually oblivious to the fact that the construction is on-going and situation-dependent.
     It can be argued that “not knowing” is actually a very high state of being, allowing for wonder, mystery, and surprise. “Not knowing” allows us to look at what is actually before us with a minimum of assumption – to see and experience what we would otherwise miss, because of preconceived ideas and expectations. “Not knowing” is what allows a child to be fascinated by something an adult sees as ordinary. “Not knowing”, in Zen circles, is called “beginner’s mind”. As Gil Fronsdal says above, "An expert may know a subject deeply, yet be blinded to new possibilities by his or her preconceived ideas. In contrast, a beginner may see with fresh, unbiased eyes."