I agree with a caveat, the disagreements come in the realm of the minor change, not the big stuff. If one changes the volume setting on your amp, everyone always hears a change. It is real, quantifiable and immediate. If one changes a cable, one either gets a similiar result for the vast majority of folk listening or they don't. The change really become one of perception when the majorty of folk do not hear any difference unless someone else, a third party, tells them what to hear. Then we are into the herd mentality where no one wants to be considered an idiot by the 'experts' so they tend to also claim a change. The third type of change is the imaginary one where 9 out of ten folk will hear nothing on their gear, no veils lifted, no fog removed, nothing at all, unless told what they are supposed to hear. I find this sort of change bordering on snake oil.
For hundreds of our years of history patent medicine folk made a living traveling around the country claiming amazing cures from simply taking their product. They sold a lot of the stuff and a whole lot of folk claimed to have had their health improved. Today we know that the vast majority of effect of those products was due simply to the high alcohol content in the 'medicine'. Todays snake oil salesmen are found in abundance in high end audio. The placebo effect coupled with mass hypnosis does produce a lot of claims of audible improvements that might just not really be there.
If one needs to study and listen in a special way to hear a change, is the change there? If a tree falls in the forest and an audiophile is not present, did God get the 'timber 'right?