Masked man fallacy
Also known as Intensional fallacy
Logical fallacy
The masked man fallacy is a reasoning error where two things are judged to be different only because you believe different things about them. It is named after the argument: I know who my father is, I don't know who the masked man is, so the masked man is not my father.
In everyday life
Someone reasons, 'I trust my bank, and I've never heard of the company behind this app, so the app can't belong to my bank', when in fact it does.
You insist your favorite author could never have written a mystery novel you disliked, because you have never heard of the name on its cover, and then learn it is the author's pen name.
Why your mind does this
Our ancestors survived by spotting patterns fast: rustling grass might mean a predator, and dark clouds meant rain. Filling gaps with a plausible story lets us act on thin information instead of freezing. A brain that sometimes sees a pattern that isn't there loses less than one that misses a real threat.
Its family, in 30 seconds: Stories & patterns
How to spot it
Watch for the step where 'I think one thing about this and another about that' turns into 'so they must be different things'.
How to counter it
Separate what you know about something from what it actually is, and check whether two descriptions might point to the same thing.
Same family: Stories & patterns
SourceWikipedia