Being a diver (relatively new-60+ dives) and a clinical psychologist, this post caught my interest. I'd like to make a couple comments:
First, learning via books and research (no matter how thorough) and learning by experience are not interchangable. They are certainly both powerful and important but they are practically and, more relevantly to my point, neurologically independent. That is, different parts of the brain are utilized for each, and you can independently acquire one form of 'knowledge' without the other. (note that this point, as others below, are empirically demonstrated through research.) What is also true is that, while they can be acquired independently, each is necessary to any valid assertion of what is commonly referred to as 'knowing' something, since even a full (impossible, in any case) knowledge in only one domain remains and incomplete knowledge of the topic of interest. So it is theoretically possible to know, via study, everything written or said about a topic, and yet remain quite ignorant (practially and neurologically). The converse is also true about experience; a thousand dives may not teach you what is in one SB post. since it seems obvious that no one is taking either extreme position in the forum, it is a matter of personal perspective, and thus degree, that is being argued.
Second thought: That 'you don't know what you don't know' is necessarily (i.e., logically) true. More relevantly, and in hopefully more helpfully phrased... while we can learn/understand that we do not know everything within an area of study, we necessarily remain ignorant of which particular items or facts, or how many, within a topic that we don't know, and thus remain unable to assess our degree of knowledge or ignorance with any degree of certainty. It seems to me to this factor that is being referred to in the forum. This is why people assert that continued learning is essential, whether they come down on the side of research or of experience.
Third observation: Humans as a species are very poor at risk assessment. This appears to be the case whether or not we have recieved specific education-or experience-at assessing risks. This is, in part, because we are not very competent with statistics and/or research, combined with the fact that we are motivated by the part of the brain that processes emotions - contrary to Aristotle, we are not rational beings, we merely have the capacity for reasoning. Our cortex ('rational' mind) facilitates the pursuit and obtaining of our goals, but our limbic system ( simplistically speaking, our emotional processor) determines our goals. Whether we use reason to check/balance/regulate our emotions/goals in any given instance is individually determined (and obviously some are better at it, or more interested in it, than others). Further, what goals we have are also individually determined. In terms of the forum, it seems to me that the discussions including 'risk-assessment' and 'risk-tolerance' as factors the foregoign: we are not good at it, though we can get better, and what constitutes risk and acceptable risk is emotionally more than rationally derived.
Summary? We need to have both 'book' knowledge (i.e., knowing 'that') as well as experiential knowledge (knowing 'how') if we wish to (justifiably) assert that we know something well. We need to really understand that no matter the domain, even with the above, there is a great deal we don't know, and 'don't know we don't know.' Unless, of course, we like to eat crow when we finally manifest our ignorance (for example, on a SB post or in an obituary). As is said, ignorance of our own ignorance is truly ignorance. Finally, we need to work consciously and hard to counteract our relative genetic incompetence at risk assessment, which is amazingly compromised by the fact that we are emotionally invested in our goals...like going diving.
Why do people go way beyond their training/competence? Because we want to, and because we don't actually understand why or when we shouldn't. But i would suggets that the most powerful counter to the impulse, whenyou see it in others, is peer pressure and modeling. Don't agree, don't support, don't aquiesce, don't keep your mouth shut, and most certainly don't go with them. While those who know that they don't know can be taught, both bravado and arrogance tend to dissipate in the absence of an audience.
Anyways, some thoughts of mine. Mark.