It's while packing for a trip that one is really hit by the ubiquity of the phenomenon of how an item which has always been kept in a particular place just won't be there. It just ... vanished.
For years I had some out of circulation British currency notes that I meant on a future trip to take to the Bank of England main office and trade them in, which is the only legal thing you can do with them. They were in an envelope in the back of a particular drawer, and I frequently saw them there, but when I finally was to return to Britain and went to take them, they weren't there. They just ... vanished. They haven't reappeared in the year and a half since then, either.
A few months ago I bought a new pair of suspenders. I put them on top of my dresser and frequently saw them there. I meant finally to use them on this trip, but they aren't there. They just ... vanished.
A set of three toiletry items, not easily or inexpensively replaced, that I took on my last trip I left in my travel bag, and saw them there last week when I peered in needing something else. When I went through the contents today, they're not there. They just ... vanished. All three of them. They're not in the only place I ever keep them when they're not in the bag, either.
A few weeks ago I got my car registration renewal. I needed a smog check. I stuck the notice in the glove compartment, hoping to find time in an excessively busy current schedule to get it done. I took the car in to the dealer for pre-trip servicing early this week. After we'd finished going over the rest of the job, I asked, "Do you do smog checks?" The adviser said, "We do. Got your paperwork?" Oh, it was there. He took it and then gave it back. But when I got home and prepared to mail it in ... it had vanished. I'd had it tucked in to the book I was reading. It wasn't there. It wasn't with all the paperwork I got from the dealer. It had just ... vanished. Fortunately there's now a kiosk in the supermarket to do instant reg renewal with a credit card, and it doesn't require the paperwork or its vital printed barcode.
Sometimes things that just vanish eventually turn up. Often right where they were all the time. Other times they don't. Once, some years ago, tired of losing eyeglasses, I ordered two new pair instead of one. Now I had three and was well prepared. Within weeks all three had ... vanished. At home: I didn't leave them out somewhere. None of them ever turned up, not even when we moved house.
Why do things vanish? Are the cats playing tricks on me? Are burglars sneaking in when we're not home? (Possible with the money, even though it'd do a home-grown burglar no good, but then why didn't they take ...) Are there holes in space, or can the items actually take themselves off? In some cases I can move something absent-mindedly, and indeed there are many times when I think, "I put this somewhere, but I can't remember where." But in the case of the three items I need for this trip, that's emphatically not so. It's a mystery.