> what humans can realistically create with their own hands from nothing

could medieval blacksmiths really create a sword from nothing but their own hands? how would they get the iron? would they have the knowledge locate veins of iron and then mine that iron? could they build the kiln and forge the equipment necessary for forging

arguably, by this standard, even farmers could not farm. farmers may know how to plant their crops, but without current crops to gather seeds from, would they know how to find the strains of plants that suit farming and then gather the seeds from those plants?