We've all been there before. You take the clothes out of the dryer, start folding, and you're left with one lone sock. You retrace your steps from the laundry room, thinking you may dropped it, check the dryer again and the laundry basket, but it's no use. The sock is gone. You continue to look for it over the next few days, but still find nothing. You wonder to yourself. "Where could it have gone?" But maybe the question you should be asking is, "WHEN could it have gone?" (I wish dramatic music could start playing right now.)
Imagine this: Socks are all part of a quantum leap/time travel experiment which periodically sends them on super secret sock missions. (Say that 10 times fast) So when your sock goes missing it is actually traveling through time solving worldly problems. I know what you're thinking. Time travel should allow the sock to return exactly when it left without anyone knowing. You are correct. But what if the sock, let's call him Sock Bakula for fun, is stuck in a perpetual quantum leap, leaping from one time to another, unable to come home until he fixes another problem. At any given time your sock could be in the old west, communist Russia, ancient Rome, etc.! It's all very exciting. Imagine how many heroic socks are sitting in your drawer right now. But, eventually, Sock Bakula gets out of his perpetual leap and returns home. That's when out of the blue, we find the sock and are overjoyed to pair him up with his lonely partner.
But that's just a theory. We'll probably never know for sure.