精益求精 Already fine, and seeking finer still. From Zhu Xi’s note on a line in the Analects: those who work bone and horn cut and then file, those who work jade and stone carve and then polish, “already fine, and still seeking finer.”
一丝不苟 Not careless by a single thread. Conscientious down to the smallest detail. The dictionary cites the novel The Scholars: “When the superiors learn of it and see that he is not careless by a single thread, promotion is near.”
推敲 Push and knock. The poet Jia Dao could not decide whether his monk should push or knock at the gate under the moon. Han Yu told him that knock was better. The word now means to weigh words with care.