This is a short coda to the Modernisms series.
Misplaced assumptions can trip you up - you have to know to take the game world as it is, and find out how it is before errors kill your PC.
But that's not to say all anachronisms and modern assumptions are out of place.
What if the world deliberately brings in out-of-period elements and caters to assumptions of a modern world?
You can see this in my Felltower campaign with its assumptions on race and gender. It's easier and more fun, and feels better, to play a game where unfair treatment by gender and racial identity are both aberrations if they show up at all. This is something I've found players assume will be the case . . . so I cater to it.
Doing so makes the game easier and more fun.
Ones that don't really make the game more fun - say, massive modern-style conflicts with full-nation-power mobilization and total war - fall under areas that the players need to be aware of.
It's a fairly basic game approach. If it makes the game better, keep it or add it - or cater to it, if it's assumed. If it does not, or lack of it makes the game better, keep it out or remove it. That has to be for the GM and the players, because if one or the other are unhappy, the game will likely fail.