Or maybe we can call it an “invariance delusion”. The art of assuming all other things will stay the same when they obviously won’t
It occurs to me that the common contemporary expression is probably cerasus legendo.
Complete tangent: I worked with a guy who was doing ‘full contact’ exercise boxing. Which is like real boxing, except that the people doing it aren’t boxers. And he reported that normal people are surprised when you hit them. “You could see the surprise in their face: ‘You hit me!’. Yes, and I’m going to hit you again if I get a chance…”. Also apparently a thing with women’s boxing: “boxercise” is not the same as boxing, and a significant number of women who try to make the step aren’t ready for it.
Or aren’t stupid enough for it, given the increasing knowledge we have about head knocks and permanent brain damage
Also that, but there is a chunk of amateur boxing where hits to the head are just banned. Boxing is defined by not being allowed to do hits to areas outside the hit zone, and only with the glove, etc, so ‘no head punches’ is just a further refinement of the rules.
Still don’t have a good answer but I thought I’d post this link to Goodhart's law - Wikipedia since it further links to several examples that seem somewhat related to what the OP is looking for. In particular Reflexivity (social theory) “refers to circular relationships between cause and effect” seems in the ballpark.
Not exactly what you are looking for, but I think the Dunning-Kruger Effect. is pretty close.
Goodhart’s law is certainly a good example of the phenomenon we’re talking about.
This sounds like some variant of the Ludic Fallacy, where it’s the second-order consequences that are the “unknown unknowns” of that fallacy.
Random thought: “The Fritz Leiber” fallacy - so called because Fritz Leiber wrote a novel called “You’re All Alone” (or “The Sinful Ones,” if you want a lurid cover and the vague implication of naughty business) in which the main character steps out of his usual role in life, and everyone else just acts as if he’s still there, happily exchanging small talk with the empty space where the main character should have been, etc. Murray Ewing.co.uk — Mewsings — You’re All Alone/The Sinful Ones by Fritz Leiber