Possible test to check whether X is your crux for believing Y: ask yourself, if you found out X was false, would it make you say "holy fuck, I must be wrong about Y!!"?
That is: would you happily admit that Y must be false too? Would you feel glad you noticed X was false, because it set you straight about Y?
Example where the answer is "yes" for me: I think physics is a serious field of study with reasonable standards for publishing. As a consequence, I think a non-physicist wouldn't be able to get a parody paper published in a reputable physics journal. But if someone succeeded in doing that, I would go "holy fuck, I must have been wrong about the field!!".
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If instead the prospect of being wrong about X makes you feel angry, worried, or defensive about Y, then maybe that's because you're imagining that you'd still believe Y, and that you'd see X turning out false as just an infuriating coincidence that other people will use an excuse to doubt Y. If that's how you'd feel, then X probably isn't a crux for you.
Example where that's how I'd feel: I also think that physicists would probably fare better than laypeople at learning Chess. That is, if you take a bunch of physicists who don't play the game at all and a bunch of laypeople who don't play it either, and gave them each three months to get good, I think the physicists would end up stronger. That's because I think physicists are just generally smart and serious people, and I think being smart and serious are huge boons for learning Chess quickly. But if someone did this experiment and I turned out to be wrong, I would roll my eyes and feel hurt about it. It would make me want to say "I guess Chess is a stupid game that you can get good at by being stupid just as well as by being smart". I wouldn't feel like physics had been debunked; I'd feel like it had been attacked. Not a crux.
Side note: I'm a little unsure how I feel about that last example, but I'm posting anyway because Quick Take.