Before getting into the details, let me briefly sketch my target.  The principal target of my skepticism about introspection concerns large-to-medium-sized structural features of currently ongoing conscious experience.  An example of what I'm not skeptical about is this: If you think you're thinking of a banana, probably it's true that you are thinking of a banana.  The introspective judgment "I'm thinking of a banana" might even contain within it the thought of a banana, making it automatically self-fulfilling.

However, what you don't know so well, I've argued, are the structural features of that thought, for example, whether it is in inner speech (words you silently speak to yourself), or inner hearing (auditory imagery that is experienced as being more passive than inner speech), or whether it is to some extent also, or instead, an imageless/wordless "unsymbolized thought", or....  Even if you might rightly be confident about the coarsest-level distinction here -- for example, that it's a thought specifically in inner speech as opposed to some other modality -- the basic structural features of that inner speech experience can be difficult to know.  Is the speech at a normal pace relative to ordinary speech or does it transpire more quickly?  Is the speech experienced as located somewhere, e.g., in the center of your head, versus somewhere else or nowhere?  Is there some distinctive feeling of understanding that accompanies the inner speech?

Alternatively, consider your current visual experience.  How stable is it?  How clear and distinct are shapes and colors in the periphery?  It is in some respect flat, like a photograph, or does it have some real depth beyond what is possible in a photograph?  If the latter, does the depth of it change dramatically when you close one eye?

You might not be convinced that introspection of the large-to-medium-sized structural features of your ongoing conscious experience is as difficult as I suggest.  But hopefully you at least have a sense of what my position is.  Now, to Sahar's question.  Why is it so difficult?  In the interview, I listed three reasons.  Here, I'll expand those reasons into five.  None of these reasons, by itself, needs to make introspection super difficult.  But combined, they create quite a set of obstacles to good self-knowledge.

First, experience is fleeting and changeable – or so it seems to me right now as I reflect, introspectively, upon it.  The screen of text before me, as I reread these paragraphs, is relatively steady; but my visual experience as I look at the text is in constant flux.  As my eyes move, the portion that’s clear, the portion that’s hazy, constantly changes.  I blink, I glance away, I change my focus, and my experience shifts.  My eyes slowly adapt to the black and white of the screen, to the contrast with the surrounding desk, to the changing light as the sun goes behind a cloud.  I parse some bit of the page into familiar words as my eye scans down it; I form a visual image, reflecting the content of the discussion; my attention wanders.  All this, it seems, affects my visual experience.

Consider your own experience as you read this paragraph.  The text in your hands changes not a whit, but your visual phenomenology won’t stay still a second, will it?  (Or will it?)  The same is true, I’m inclined to think, for our auditory experience, emotional experience, somatic experience, conscious thought and imagery, taste, and so on: Even when the outside environment is relatively steady, the stream of experience flies swiftly.  It won’t hold still to be examined.

Second, we’re not in the habit of attending introspectively to experience.  Generally, we care more about physical objects in the world around us, and about our and others’ situation and prospects, than about our conscious experience, except when that experience is acutely negative, as with the onset of severe pain.  This may seem strange, given the importance we sometimes claim for “happiness,” which we generally construe as bound up with, or even reducible to, emotional experience – but despite the lip service, few people make a real study of their phenomenology.  We spend much more time thinking about, and have much subtler an appreciation of, our outward occupations and hobbies.  And when we do “introspect,” we tend to think about such things as our motives for past actions, our personality traits and character, our desires for the future.  This is not the sort of introspective attention to currently ongoing (or immediately past) conscious experience around which my skepticism turns (though I am also skeptical of much of this purported knowledge, on different grounds).  Introspective attention to experience is hardly a habitual practice for most, perhaps any, of us, except maybe a few dedicated meditators of a certain sort.

If accurate introspection requires a degree of skill, as I suspect it does, in most people the skill is uncultivated.  Furthermore, relatedly, experience is difficult to remember: Generally what we remember are outward objects and events – or, rather, outward objects and events as interpreted, and possibly misperceived, by us – not our stream of experience as we witness those objects and events.  We remember, usually, that the boss said the work wasn’t up to snuff, not that our visual experience as he said it was such-and-such or that we felt some particular sinking feeling in the stomach afterward.  These conscious experiences fade like dreams in the morning unless, as with dreams, we fix them in mind with deliberate attention within a very short space.  

Third, in part due to our disinterest in conscious experience, the concepts and categories available to characterize conscious experience are limited and derivative.  Most language for sensory experience is adapted from the language we use to describe outward objects of sensation.  Objects are red or square or salty or rough, and usually when we use the words “red” and “square” and “salty” and “rough,” we are referring to the properties of outward objects; but derivatively we also use those words to describe the sensory experiences normally produced by such objects.  That’s fine as far as it goes, but it’s prone to invite confusion between the properties of objects and the properties of experiences of those objects.  The practitioners of certain specialties – for example, wine tasting and sound engineering – have refined language to discuss sensory experience, but even here our conceptual categories are only rough tools for describing the overall experience.  And, anyway, isn’t the gustatory experience of eating a burrito as complex as that of tasting a mature wine, and the auditory experience of sitting in a restaurant as complex as that of hearing a well-played violin?  We almost completely lack the concepts and competencies that would allow us to parse and think about, talk about and remember, this complexity.

Fourth, the introspection of current experience requires attention to (or thought about) that experience, at least in the methodologically central case of deliberately introspecting with the aim of producing an accurate report.  Problematic interference between the conscious experience and the introspective activity thus threatens.  Philosophers and psychologists going back at least to August Comte have complained that the act of introspection either alters or destroys the target experience, making accurate report impossible.  Much of experience is skittish – as soon as we think about it, it flits away.  Suppose you reflect on the emotional experience of simple, reactive anger, or the auditory experience of hearing someone speak.  Mightn’t the self-reflective versions of those experiences – those experiences as they present themselves to concurrent introspection – be quite different from those experiences as they normally occur in the unselfconscious flow of daily life?  A number of psychologists have attempted to remedy this difficulty by recommending immediate retrospection, or recall, of past experience rather than concurrent introspection as the primary method (e.g., James, 1890/1981).  However, deliberately poising oneself in advance to report something retrospectively may also interfere with the process to be reported; and if one only reports experiences sufficiently salient and interesting to produce immediate spontaneous retrospection, one will get a very biased sample.  Furthermore, retrospection is likely to aggravate the fifth problem, namely: 

Fifth, reports of experience are apt to be considerably influenced, and distorted, by pre-existing theories, opinions, and biases, both cultural and personal, as well as situational demands. The gravity of this problem is difficult to estimate, but in my opinion it is extreme (and considerably larger than the influence of bias and preconception now generally recognized to permeate science as a whole).  Given the changeability and skittishness of experience, and our poor tools and limited practice in conceptualizing and remembering it, we lean especially heavily on implicit assumptions and indirect evidence in reaching our introspective and immediately retrospective judgments.  One major source of such error is what the introspective psychologist E. B. Titchener called “stimulus error”: We know what the world, or a particular stimulus, is like (we know for example that we are seeing a uniformly colored red object), and we are apt to infer that our experience has the properties one might naively expect such a stimulus to produce (e.g., a visual experience of uniform “redness”).  We’re much better accustomed to attend to the world than to our experience, and the difference between sensory attention to outside objects and introspective attention to the sensory experience of those objects is a subtle one; so the former is apt to substitute for the latter.  Even when experience isn’t so easily traceable to an outside object, I’m inclined to think our theories can profoundly affect our reports.  If we think images must be like pictures, we’re more apt to instill reports of imagery with picture-like qualities than if we don’t hold that view.  If we think cognition takes place in the brain, we’re more apt to locate our cognitive phenomenology there than if we think it takes place in the heart.  If we think that memories must be imagistic, we’re more apt than those who don’t think so to report memory images.

Experience is a fast-moving chaos -- a tornado whipping through a magnet factory.  If we approach it without practice and skills, with derivative, second-hand concepts, and with our attention split between the experience itself and the act of trying to figure out what that experience is, no wonder we make a mess of it.  We end up describing at least as much what we expect to be there as what is actually there.