I am beginning to suspect that it is surprisingly common for intelligent, competent adults to somehow make it through the world for a few decades while missing some ordinary skill, like mailing a physical letter, folding a fitted sheet, depositing a check, or reading a bus schedule. Since these tasks are often presented atomically - or, worse, embedded implicitly into other instructions - and it is often possible to get around the need for them, this ignorance is not self-correcting. One can Google "how to deposit a check" and similar phrases, but the sorts of instructions that crop up are often misleading, rely on entangled and potentially similarly-deficient knowledge to be understandable, or are not so much instructions as they are tips and tricks and warnings for people who already know the basic procedure. Asking other people is more effective because they can respond to requests for clarification (and physically pointing at stuff is useful too), but embarrassing, since lacking these skills as an adult is stigmatized. (They are rarely even considered skills by people who have had them for a while.)
This seems like a bad situation. And - if I am correct and gaps like these are common - then it is something of a collective action problem to handle gap-filling without undue social drama. Supposedly, we're good at collective action problems, us rationalists, right? So I propose a thread for the purpose here, with the stipulation that all replies to gap announcements are to be constructive attempts at conveying the relevant procedural knowledge. No asking "how did you manage to be X years old without knowing that?" - if the gap-haver wishes to volunteer the information, that is fine, but asking is to be considered poor form.
(And yes, I have one. It's this: how in the world do people go about the supposedly atomic action of investing in the stock market? Here I am, sitting at my computer, and suppose I want a share of Apple - there isn't a button that says "Buy Our Stock" on their website. There goes my one idea. Where do I go and what do I do there?)
It's still hard to tell what exactly you're doing, but I'll try to spell out how I do it.
Lay the duvet flat on the bed with the top edge towards you, and then lay the inside-out cover flat on top of it with the opening towards you.
Stick your arms into the cover up to your elbows and grab the sides of the cover from the inside. Hold on to the sides and pull your arms most of the way back out, gathering the fabric towards you. Keep going until you can reach the corners.
Holding the corners from the inside, bring your hands up to shoulder height and shake them slightly until most of the fabric is draped around your elbows.
Grab two corners of the duvet through the cover. Still holding the corners, pull your hands together, gathering the duvet between them. Pull the whole edge of the duvet through the cover opening.
Lift your arms over your head, then shake them slightly as you move them apart, keeping them over your head. The cover should drop partway over the duvet.
Forcefully bring your arms down. WOOSH!