Potsherd
A potsherd is a broken fragment of earthenware. The two scope verses use it in two different ways — once as a literal household object pressed into service in extremity, once as a figure for human smallness over against the Maker.
A Tool in Affliction
Job, struck with sores from sole to crown, takes up the most expendable thing at hand: "And he took for himself a potsherd to scrape himself with it; and he sat among the ashes" (Job 2:8). The fragment is what is left when a pot has already been broken; reaching for it places Job among the ash and the rubble of his own household.
A Figure for the Creature
Isaiah turns the same broken fragment into a metaphor for the creature who quarrels with God: "Woe to him who strives with his Maker! A potsherd among the potsherds of the earth! Will the clay say to him who fashions it, What do you make? Or your work, He has no hands?" (Isa 45:9). The image trades on the ordinariness of the shard. One piece of broken pottery has no standing to interrogate the potter; one human, set among countless others on the surface of the earth, has no standing to indict the Maker.