小人閑居して不善をなす
(Shoujin kankyo shite fuzen wo nasu;
“The mean, when idle, accomplish ill”)

Definition:

Idle hands are the devil’s workshop. Mean-spirited or narrow-minded people will do harm when given free time and left to their own devices.

Breakdown:

We begin with the noun 小人 (shoujin), literally “small person,” by extension “small-minded person,” “mean person.” Particles are elided, but one may imagine the shoujin as the topic or subject of the sentence. What follows is noun 閑居 (kankyo) “idleness,” turned into a verb by attaching the verb する (suru), “to do,” in conjunctive form as して (shite, rhymes with bidet). This is followed by a second clause in an implied conditional or hypothetical relationship, beginning with the noun 不善 (fuzen), literally “not-good,” i.e. “evil deeds,” or more gently “mischief.” This is marked by the particle を (wo) as the object of the verb なす (nasu), “to accomplish,” “to do,” which appears in conclusive form. 小人 carries forward as the implied subject of the verb.

Notes:

There’s a distinct classist sort of prejudice embedded in the history of this phrase: 小人 can refer to the “common folk” and in that sense is considered an antonym of 君子 (kunshi), the “wise prince.” That said, the same could be said of English: “mean” means “cruel” now, but used to mean “common,” while even “villain” comes from a term meaning “farmhand.” It turns out that rich people deciding baselessly that they’re the good guys, while the common folk are morally deficient, is an old and widespread phenomenon. Somewhat ironic, given that the rich tend to be far more idle (and to cause far more harm on a per capita basis!) than everyone else.

In any case, in modern usage this kotowaza has lost the classist nuance, and is mostly a warning against the dangers of lazing around rather than working.

It is acceptable, but rare, to write nasu as 為す. Interestingly, kankyo was originally written as 間居, but now 閑居 is the standard rendition in Japanese. On the other hand, writing fuzen as homophone 不全 (“incomplete”) is an error; so is pronouncing 小人 as shounin.

This phrase comes to us from the Confucian text, the Great Learning (Japanese 『大学』 = Daigaku). The Japanese rendition actually says …為せば至らざる所なし (naseba itarazaru tokoro nashi), “when [the mean accomplish ill], there is no place they will not arrive.” That is, there is no limit to the bad things a bad person will do if given the time; no lengths they won’t go to. (This longer version is not used as a saying.)

Example sentence:

「小人閑居して不善をなすというけど、悪徳な資本家達は引っ切り無しにパーティーやらゴルフやらの暇つぶしばかりをしているくせに、庶民のための公的支援は絶望しそうなくらいに妨害してくる」

(“Shoujin kankyo shite fuzen wo nasu to iu kedo, akutoku na shihonka-tachi wa hikkiri nashi ni paatii yara gorufu yara no himatsubushi bakari wo shiteiru kuse ni, shomin no tame no koutekishien wa zetsubou shisou na kurai ni bougai shite kuru.”)

[“They say that idle hands are the devil’s workshop, but it still brings me to despair how the robber barons keep blocking public assistance in spite of the way they’re constantly just killing time with parties and golf and the like.”]