There are two types of sheet people in this world: people who sleep with a top sheet, and people who don't sleep with a top sheet.
Top sheet proponents, like this stock model, think the no-top-sheet approach is crazy. Sheets come in packs and there is a top sheet in the pack for a reason.
But apparently some people like to sleep with just a comforter or blanket, or even ~nothing~ on top of them.