Interesting thread, JJJ!
This is an interesting study on human perceptions, truth, and science.
Up until reading this, I've actually had the assumption that divining or dowsing was valid, and worked reliably. This was based purely on limited information, and never having researched it. I just assumed it was the result of some well-understood physical phenomenon that I had never gotten around to reading up on. I wasn't even aware that the scientific community discounted it, or that it "only works for some people." The fact that I was ignorant in this didn't matter, since it had no bearing on my personal sphere of existence (i.e., I don't think my life would have been any different up to this point if I had known or thought otherwise, apart from the indirect differences via the Butterfly Effect).
When I was about 16, several classmates and I had the job of digging a trench so that a broken water line could be repaired. The water line was a PVC pipe about 4 inches in diameter, buried about 5 feet underground. I believe it ran about 200 to 300 feet across a field. Someone there (probably the property owner) had a pair of "divining rods". They were L-shaped pieces of heavy wire, with the short leg about 5 inches and the long leg about 12. We all took turns "divining" at different points along the water line. You'd hold the short legs in loose fists, with the long legs pointing forward. When you walked across the water line, the rods would swing towards each other. We'd then put a stake in the ground at this point. We continued down the length of the pipe this way, taking turns, putting in a stake every 20 feet or so. We then started digging the trench in the middle, and worked outwards until we found the break in the pipe. The stakes were within a couple feet of being directly over the pipe.
It was likely this experience that left me with the assumption that divining is a valid, reliable process. After reading the info in this thread (especially the article pt linked to), I now think it's probably myth, and the "idiomotor reaction" mentioned sounds to me like a reasonable explanation.
When it comes to my own conclusions and beliefs, I'm a "fuzzy logic" kinda guy. In this particular example, I now have about 98% confidence that divining or dowsing doesn't work. But that other 2% is still there.
I agree with Oberon's comment about the "we now know" statements that are often heard. I understand that it's not really practical to always say "we now think". Since we can't ever really know anything with 100% certainty, there wouldn't be much point even having the word "know" if it has zero domain to be applied to. So it's just generally understood that the word "know" really means "pretty damn certain".
Still, I think there's a subconscious effect that happens when we use and hear the "know" verbiage. It tends to make people closed to the concept that we could conceivably be wrong, even though, as repeatedly demonstrated, we can be. I think this kind of inflexible certainty can slow scientific progress and discovery.