It’s pure psychology.
Suppose someone just shelled out $6000 for a 100 gram can of rhino horn powder because he has a firm belief in it’s aphrodisiac powers. He’ll be happy with the purchase.
Others, who never tried rhino horn powder themselves, may warn him he’s being scammed. And yes, he may think that annoying because he’s perfectly happy with his purchase. And maybe it even worked, that’s the power of our mind. And if it didn’t, he’ll probably never admit it ... he’ll still write raving reviews.
How bad is it that some rational thinking people doubt the use of rhino horn powder because it’s totally unclear if and how it works and it has never been scientifically proven?
I know, I know ... even if things can not be scientifically proven or can be measured, we still can hear differences in audio ’quality’.