In medieval times, poverty was so great, people wore only old sacking and sheep, and had no other possessions, so were extremely vulnerable to home attacks. The main risk was from robbers, after the only thing the poor had in abundance, which was silence and nothing, as silence is golden, and nothing is worth more than silver.
Self defence was made difficult because of the wriggling jumper, so on hearing intruders, the poor tied flat wood to their feet so that they could balance, and the wood also served as a weapon. Thus attired, they could chase off the attackers, with blood curdling screams of 'shoooooo'.
This lead to footwear being called 'shoos'. 'Pass me my shoos Boedicia' they'd say silently, "they've come to take nothing from us."