Someone should write a book called Household Chores for Hackers: The algorithms your mother took for granted and forgot to teach you.
https://www.amazon.com/Home-Comforts-Science-Keeping-House/d...
I think my parents' generation viewed duvets as unacceptably decadent, and thought all children should learn to fold hospital corners[0] to build character.
Also, many rooms let you get the temperature to ~15C.
</ducks>
Here is a video of someone actually folding the sheet as the parent requested: https://m.youtube.com/watch?v=ckTCocBCUN4