I have one theory.
The reason the dryer always gets blamed is that in a typical washer+dryer side-by-side configuration, you throw everything into the dryer and don’t notice the missing sock until sorting stuff out of the dryer. In actual fact, I suspect a washer is just as capable of sending lone socks into the fifth dimension as a dryer is.
One way I solve this perennial problem is by having many socks in just a couple of solid colours. That way, when one inevitably gets sent to another dimension, I simply have an odd number of one particular set. And since it’s bound to happen again, I’ll be back to an even number. It all works out.
Indeed. In fact, a leading theory is that the lost sock phenomenon is due to [warning: physics puns ahead] parity breaking during the spin cycle.
How come nobody ever finds a missing thing in the next-to-last place they look for it? 
Look what I found in my laundry basket:
Wow !
That’s spooky.
I did laundry yesterday; pulled a single wool sock (that was worn < 24 hrs earlier) out of the washer. I searched everywhere for it’s solemate ::groan::. Pulled everything out of the dryer & inspected each item to see if it crawled inside a shirt or something. No joy. Searched around the washer & dryer, Nada. Even searched downstairs. Nuffin’.
Then I went into the spare bedroom to fold/put away the pants that had been hanging there since the last time I did laundry (no comments!); brought them over in front of the washer & dryer to take the hanger off & put it away before folding. Look down to fold them & what is right in front of my toes? A wool sock; look on top of the washer where I see it’s (wet) mate.
I looked at the floor multiple times; I even searched around the washer in case it fell to the side. It. Was. Not. There! The sock was not even in the same room as the pants were; therefore, there is only one possible explanation. I know the creatures that live in the basement are hobgoblins (because my sister told me so when I was a wee Spiderboy). What is the name of the creatures that live in the attic; are they hobgoblins, too or something else? It’s very clear that they took it & then dropped it from the attic access panel when I wasn’t looking!
Those are ceiling sprites and if you have cats and see them staring at the ceiling at nothing, now you know why – although the cats are the reason the sprites are there in the first place. A vicious cycle, it is.
… and one that’s missing a valve stem cap, if memory serves.
So, a funny thing just happened. My stepdaughter stopped by after work to pick up her son, and also grab some Thanksgiving leftovers. All of the leftovers were in identical plastic containers with lids – I save the plastic containers that I buy lunchmeat in and use those for storing leftovers. My wife pulls a stack of, oh I don’t know, 8 or 9 different containers of leftovers out of the fridge, and starts combining parts of different containers. So in the end she has three containers to give her daughter and the rest go back in the fridge for us. She starts putting lids back on everything – and is somehow one lid short. Stepdaughter and I were both standing right there at the counter watching her, and none of us has any idea how we came up missing a lid.
Check the dryer.
I’m sitting here wearing mismatched socks and being amused by this thread.
Check your navel. Now check it again.
I’ve got it.
I’ll drop it in the mail to you. It’s the least I can do.
I’m guessing something got double-lidded.
It’s an instance of Sam Loyd’s “get off the earth” puzzle.
When you move the lids around, there will be 1 fewer lids.
This deserves applause. One of the many reasons I come here is for one-liners like this. Kudos to you, sir.
I know you all have been losing sleep over the fate of my wedding ring, as I have, so here’s an update:
I found it! And I wasn’t even looking for it. But it was in the most obvious possible place. I don’t know why I didn’t look there first!
The freezer. I was putting away some groceries, and as I moved some items I heard a metallic clatter. I pulled out a package, and there it was, sitting on a shelf. I have no idea how or why or when it came off my hand, other than it happened sometime before my first post in this thread.
I was reasonably sure I’d eventually find it, and this time it only took three weeks. Last time it was about three months. If anyone’s interested, I can tell the story of how a ring lost in Maryland (probably) turned up in a motel room in South Dakota.