I have a double bed pushed up against the wall in my room, and I find it very difficult to get the bed sheet properly tucked in while changing the linen. I looked in vain for that holy grail of inventions; the fitted sheet, because I know we have some somewhere, but alas, no luck. So resolved, I strip the sheet off my bed and struggle on with putting a normal sheet over the mattress.
Hurrah, a sense of achievement comes over me, my sheet is changed. But then I look down to see a clean, neatly folded sheet on my chair. Oh. I have taken the dirty sheet off my bed, and put it strait back on again. Back to square one.