Have you ever had a discussion with someone who never lets you convince them on some matter no matter the strength of the evidence? What's going on when people, even perfectly sane, otherwise rational, and sincere people give excuse after excuse as to why the evidence and argument just isn't 'good enough' to compel their assent no matter its truth or validity?
Note that it is easily possible to set the bar for evidence too low, but we can also make it impossible, or virtually so, to reach.
So here, I deal with a favored rhetorical tactic of cranks, pseudoscientists, grand conspiracy theorists, charlatans of all stripes, and yes, ordinary people in everyday discussion: the Moving Goalpost.
Most people are fairly closed-minded and find changing their stance on things uncomfortable. It takes good metacognitive skills, thinking about thinking, to correct this tendency.
The fallacy takes its name from an analogy with American football, in which the goalposts are always out of reach of whoever is carrying the ball, and continue to recede further still.
With this tactic, the more unreasonable the standard of proof for refuting or confirming the claim, the better. It involves either arbitrarily redefining one's claims to put them conveniently out of reach of any disproof, or setting impossible standards from the very beginning.
The objective here is to avoid having to rescind whatever claims one is making, when one has a political, financial, personal, or ideological stake in a position. For some, no amount of evidence and reason is enough, and it shows in this use of rhetoric.
A couple of examples might be:
Show me just one experiment conducted in a lab on Earth that has ever created dark matter, directly measured gravity, manufactured a black hole, or generated controlled stellar fusion! Establishment Cosmology™ is silly, fallacious, and wrong!
This argument clearly sets impossible standards from the beginning.
It and what follows use a version of the "show me just one proof" gambit common among creationists and crank cosmology proponents (Sometimes those are one and the same!).
The next illustrates shifting standards of proof each time evidence is presented:
I want to see any example of a transitional species before I think evolution even remotely plausible! Just one!
There are still gaps in the fossil record between those and what came before and after! Where's the evidence for those??
You've filled in those gaps?
Now there are more gaps to fill! Fraud! Fake! Amoral evilutionist! Evolution is a sham!
It's important to proportion to the claim just what criteria of evidence and logic you will accept, and to stick with that as your gold standard throughout. Set reasonable standards, then admit it and change your mind once those standards have been met.
Consistency might be called the bugaboo of small minds, but it's what's needed when assessing claims open-mindedly and rationally.
Tf. Tk. Tts.