@Fredatron here in Italy duvets and other blankets are traditionally big enough to be tucked under the mattress at the feet and, at least at the beginning of the night¹, sides, so turning them 90 degrees would be quite an accomplishment, and there is also a bit of leeway² for blanket stealers to wrap themselves in the blanket while leaving at least *some* for their partners.¹ I've heard that some people manage to keep them tucked in until the morning. I'm not sure I believe that :D² *dedicated* blanket stealers can manage to steal our full-width blankets too, but it works to protect from the amateurs :D