My family members, other than me, have a dreadful time keeping their sheets on the beds. I don’t understand it. They also can’t keep pillows in pillowcases.
I depend on my bottom sheet staying in place as I have night sweats and move around a lot during the night, looking for dry fabric.
Of course, I could use safety pins to keep it in place...Maybe. Or not. They would probably spring open when I least expect it.