All four kanji represent centers—with slight differences. An axis (軸) lies inside something (a planet, feather, or scroll), as does marrow (髄) and a core (髄 or 芯). Other objects (e.g., doors) revolve around pivots (枢). The body contains specialized brain centers, as well as an axis, marrow, and a core. More abstractly, an axis occupies the center of one's existence. Also, one feels things to the core, the essence of an activity (e.g., aikido) is vitally important, and 枢 helps symbolize the center of the economy, of power, and more.

These four essays provide the key to happiness. With 暇 one has free time, whether a vacation, a leave of absence, or simply time to kill. Then 娯 provides destinations for having structured fun, including amusement parks, theaters, or venues for karaoke, pachinko, or horse races. With 愉 people relax into a carefree sense of fun and pleasure. And with 悦 one can experience joy and delight in a variety of things, including hospitality, a sense of progress, food, artistic masterpieces, a college acceptance, religious rapture, and sexual ecstasy.

A book title mentioned in the 霧 essay collectively refers to clouds, rain, and fog by citing their common "rain" radical. That unites the kanji in this bundle, as well. All four essays explore the realities of damp weather, as when fog grounds planes, frost damages crops, and people seek shelter from the elements. Because of such challenges, these characters make great metaphors. The Japanese associate 霜 with hardship; 曇 with life's ups and downs, as well as gloomy feelings; 霧 with mental fog; and 露 with transience. Because 露 symbolizes vanishing realities, that kanji in particular has inspired poetry.

Characters for body parts often feature 月 radicals. That's true here, but these four kanji have much more in common. First, limbs and joints are prone to soreness, injury, and disability, requiring various healing modalities. Second, the shoulders, elbows, and knees can show how we're relating to other people; the Japanese associate these body parts with lending support, sitting close for an intimate talk, and reining in someone's behavior. Those body parts also play roles in martial arts and sumo. Finally, one's stance can express seriousness, tension, pride, shame, discouragement, respect, remorse, or a lack of reservedness.