(Shikaku na zashiki wo maruku haku; “To sweep a circle in a square room”)
To shirk; to cut corners; to do a bad job at something because you put in the bare minimum of thought and effort. Like cleaning only the middle of a room, for show, while letting crud build up in the corners. The implication is that someone is so focused on saving time and energy that they end up doing a shoddy job even when they intend to get some actual work done.
We begin with the noun 四角 (shikaku), literally “four corners,” e.g. “rectangle,” “square,” acting as an adjective with the help of particle な (na). This modifies the following noun 座敷 (zashiki), literally “sit-spread,” but actually referring to a tatami-floored traditional Japanese room. The particle を (wo) marks this as the object of the verb 掃く (haku), “to sweep,” in conclusive form. This verb is modified by the adjective 丸い (marui), “round.” in conjunctive form and acting as an adverb. (In other words, a more literal rendition than the translation at the top would be “to sweep roundly,” perhaps.)
Some versions may use 部屋 (heya, a more generic term for “room”) in place of 座敷, or rearrange the sentence structure a bit.
(“Koba-kun, jibun no essei wo tamatama mitsuketa ronbun issatsu dake ni motodzuite kaku no wa shikaku na zashiki wo maruku haita you na, tekitou sugiru benkyou houhou desu yo. Getsumatsu made ni sankou no shiryou wo fuyashite, kakinaoshite kudasai.”)
[“Koba, basing your essay entirely on a single paper that you ran across by accident is too sloppy; you’re cutting all the corners. Gather some more material and rewrite this by the end of the month.”]