As I walk or run up the hill in the morning, catching the bus to work, I discover to my dismay that my socks are getting lower and lower inside my boots, and bunching up around my feet. This rapidly becomes uncomfortable.
Why does it occur? Obviously there is some sort of differential pulling action on my socks. I can see that down is the easiest way for the sock to move; at the outset it can’t be pulled up, for instance. But it seems that the top, at least, could still theoretically be rotated sideways. And why ould there not be a motion later that would pull it up?
Mi ne povas respondi al via demando; mi nur volas diri, ke via subskriblino placxas al mi.
LL
You mentioned gravity. The other thing working against you is the shape of your shins, getting narrower toward the ankle. To rise is thus to stretch laterally, fighting the sock’s natural tendency to resume a relaxed size.
LL:
Dankon! Gxi estas vortoj de kantajxo de la sveda rokgrupo Persone. Mi malkovris, ke, poste de nia eklernado de la internacia lingvo, mi vidis sxajne tra novaj okuloj… 
ShakenBake:
I figured as much, but I was really interrested in describing what kind of differential ankle action is necessary to selectively pill the socks…
One of two things could be going on here.
A) Your boots don’t fit. With every step your heel slides “up” your boot top, and catches your sock. When you come down on your heel again, it jams your sock down into your boot. After a couple of steps, your sock is all jammed up into your boot and none is sticking out the top.
-OR-
- Your boots weren’t killed all the way in the boot-forming process, and they are HUNGRY! Try wearing only natural fiber socks (wool, cotton, silk, bacon, etc.) and see if your boots get full.
Of course if you have little bitty bird-legs, it could be the thing ShakeNBake said. Also don’t discount L.L.'s theory. Only pay full price for THAT puppy.