Dear Morty,

I don't actually know but suspect that plectrums are made from some secret quantum supermaterial that has the ability to exploit very narrow wormholes in the fabric of space-time and disappear and reappear at random (i.e. Schrodinger's Plectrum Theory).

Regarding socks...these people appear to have the knowledge to help:

The bureau of missing socks

Best regards,

moo