Four-letter words are not always foul language: 四字熟語 and 成語

Chinese for Japanese is what Greek and Latin are for European languages or Sanskrit is for Thai and Malay: the source of a high, abstract vocabulary as well as, with a due bit of curiosity and intellectual effort, access to the wisdom of the ancients of the "Confucius say" fame.

One part of that ancient Chinese heritage are yoji-jukugo (四字熟語), delightfully laconic idioms that express very complex ideas or metaphors in mere four characters.  Using the same model, the Japanese have later come up with their own indigenous yoji-jukugo, just as succinct and sagacious as the 成語 (chéngyǔ) borrowings from China.

Quite a few of them are included in the national school curriculum and thus effectively are part of the daily vernacular. Every once in a while I post the juiciest and intellectually aesthetically striking ones here: 四字熟語/成語, so that you too can drink from that refreshing font of timeless wisdom. 

P.S. The Thai language also has a similar concept, where a four-letter, essentially four-word set expression represents a graphic metaphor, a moralistic proverb or a witty allegory. There's a plethora of such in Thai but one that springs to mind first is บ้านนอกโคกนา (ban nok khok na), literally meaning "the countryside: a chicken coop and a rice field", a both nostalgic and slightly pejorative description for where most people in this rapidly urbanising nation come from.