Ok, thanx.
I might be wrong, and I'm open to counter-evidence, but here's my proposed explanation. And the best way to convey is via example :
Using myself as an example, I've been md'ing for 45-ish years. So I've developed a keen eye for anything md'ing related. So I tend to see and notice things that the next guy simply won't notice.
For example: In my job at my street sweeper company, we used to have a string of shopping center accounts. We had to clean their parking lots each night. And I would routinely find objects of value. Eg.: A $10 bill here and there. Sometimes a piece of gold jewelry, etc.... in the middle of the night.
And one week, after I'd found 2 gold jewelry items (simply by eyeballing them), I bragged to my coworker that they had such & such melt value. But my coworkers never found as much as I did. Not that they would turn-a-blind eye to picking up something of value, but .... it just wasn't on their mind. Versus me: It was a sport. I was purposefully keeping my eyes peeled.
SO TOO IS IT WITH DOWSING ! If you are distinctly specifically going out,
looking for, and having the
expectation of finding a goodie, then go-figure : You're going to have your eyes peeled. The next guy, who WASN'T "looking" for a goodie (and hence not carrying a wand), is NOT going to be looking. And will thus not notice.
I Mean, for example, newspaper headlines sometimes have stories of persons who've accidentally stumbled on to caches. Right ? Eg.: Construction workers digging a ditch. Or someone found a false-wall during remodeling, in their old house, with a cache hidden. Therefore, go-figure :
HOW MUCH MORE-SO will there inevitably be stuff found, by persons who go out SOLELY to find things ?
So too might the explanation of your half dollar be. IF I'M WRONG, and there's some sort of quantifiable method that can be repeated (beyond random chance), then : I'm more than willing to see it demonstrated in a double-blind test.