I am not an expert but this works well enough for me.
Have the sheet open (flat) and fold in half lengthwise (or width wise up, I haven’t folded a twin in ages) over with the corners tucked into the other corners. Now it looks like two layers lying flat. I move the ends opposite the corners in so it makes a straight line that looks like a regular sheet. Now you can fold the entire length over again and then up in halves or thirds til you get a nice little rectangle.
It’s hard to describe without pictures or doing it in person. Once you get the corners tucked into each other you can fold it down to whatever size you like.
I Love You Canticle_of_Deborah...
I like your theory as a way to teach for those who have time...
I will PM you if you ask with the who/what/where/why/when.
Only if you ask.