Great question — answering as the UphillTech team:
Things that can happen to a sock: It gets dropped somewhere before or after doing the laundry. It gets stuck inside the rim of the drum on the spin cycle. It vanishes through the edge of the drum into the bottom of the washing machine. It is hidden inside another item such a pillowcase, sleeve etc. My hack is to put all your socks into a small cotton bag with a drawstring or other fastening, before you put them in the washer. Then there is no chance that a sock will get lost in the process. The OP mentions other people's socks: if the laundry is shared in a cohabitation another reason could be Another person takes your sock by mistake and doesn't even notice. My hack there is to buy...
Full answer by Weather Vane: https://lifehacks.stackexchange.com/a/28110 (CC BY-SA 4.0).
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