he one and only source of intellectual confidence is experience. Specifically, it is the understanding of wrong answers (known only to those who "do the actual work"). Thus, for every original idea on this site which I believe to be true there are perhaps one hundred bad ideas which I rejected, still know about, but do not report anywhere because it is not considered worthwhile. Who wants to wade through an encyclopedia of thoughts which even their author believes worthless?
From another direction ...
Consider the total quantity of information needed to run civilization versus the total quantity which is written down. What would you guess to be the ratio? One to one thousand? Worse?
On your own job, what could you write down to tell another guy how to do it? After reading your tome, do you think he could actually do the job? Of course not. He would typically need another two years to become comfortable with it. The extra time is needed to learn all the things you didn't write down [that you do on your job] as well as all the wrong things you tried in the past which did not work ... which he will try again because you did not transmit that information.
Here then is the source of your job confidence. The total quantity of information which delimits that job (both the thing itself and the background ... the context ... in which it is embedded).
If civilization had to be restarted from information contained in the libraries of the world alone ... we would really be in deep doodoo.
When confronted with new knowledge virtually all people look to the judgement of others to determine if that knowledge is true or not ... the experts. They have little choice. Who can know a great deal about everything?
If the knowledge of those experts subsumes the new information they may render an excellent opinion which the average citizen may rely on.
On the other hand, if the proposed new knowledge requires induction (if the new subsumes or proposes to subsume the expert's knowledge), there is a real problem.
There is no one to judge it.
It just sits there and waits for ... what? ... the opposition to die off? ... to somehow work it's way into the general intellectual life of the world? Well ... it just waits ... and waits ... until the intellectual climate is right for acceptance or trial.
There is another method of judgement.
We sense the confidence exuded by those engaged in discussion. Since we know, at least subconsciously, that confidence is an indicator of competence, we will tend to believe that individual who dominates the conversation.
Often this is true ... but not quite often enough.
If someone proposing knew ideas is seen to debate the experts, he will often look like the dummy because his confidence in new ideas is tempered by the experience of error. Most new knowledge is obtained at the expense of huge error to truth ratios. The proponent of new ideas is hobbled by knowledge of his own previous errors ... whereas the experts (who often attempt nothing new in a lifetime) have decades of book learned truths to buoy their argument without a hint of self-doubt.
Note: All "book learned" truths came from those who "swam the sea of error".
The source of my own confidence in many of the ideas presented at this site is "exhaustion of alternatives". Some things I am certain of, despite what anyone could possibly say to the contrary, because there is literally nothing left to consider. There is no way to construct an explanation in the English language which I have not considered. How do I know that I have exhausted all the alternatives? ...