Sincerity without love is a pretense.

The Book of Jin (晉書), an official history compiled in the reign of Emperor Taizong of Tang, places side by side the stories of two poor scholars. The first is Che Yin (?–401). A native of Nanping in the Eastern Jin, he loved learning from childhood, but his family was so poor he could not even buy oil for a lamp. On summer nights he caught dozens of fireflies in a white silk pouch and read by their light the whole night through. "家貧不常得油, 夏月則練囊盛數十螢火以照書, 以夜繼日焉" — his family being poor, he could not always obtain oil, so on summer nights he filled a silk pouch with dozens of fireflies to light his books, reading on from night into day. Che Yin would later rise to become Inspector of Jingzhou. The second is Sun Kang. As a man of the north, his winters were harsh. Lacking oil all the same, on snowy nights he would step outside and read by the light reflected from the snow piled against his window. "常映雪讀書" — he always read by the glow of the snow. Sun Kang too would later rise to the office of Censor-in-Chief. Later generations joined the two stories together and began to call them "螢雪之功" (hyeongseoljigong) — the achievement of firefly and snow. By the faintest of all lights, the greatest of achievements.

The English "diligence" comes from the Latin "diligentia," whose root is the verb "diligere." That verb divides in two: dis- (apart, selecting) + legere (to choose, to gather, to read). Translated literally, "to choose apart." But there is a remarkable turn. In Classical Latin "diligere" meant not simply "to choose" but, more often, "to love." The Roman poet and orator Cicero often used "diligo" of a friend — "I love (choose) him." This nuance, "to choose out of love," is the original form of diligence. The Romans, in other words, understood "diligence" not as a duty but as "attentiveness arising from affection." Latin "diligentia" therefore meant "loving care, affectionate attention." In the 11th century European monasteries taught love of Christ as a distinction between "caritas" (charity) and "diligentia" (attentive love). "Diligence" entered English in the late 13th century by way of the French "diligence." In early Middle English the sense of "loving care" was still strong. In the 14th century Geoffrey Chaucer used "with diligence" in The Canterbury Tales to mean "with loving care." From the 16th century onward, however, the meaning narrowed bit by bit into "working with careful attention," and through the 19th-century Industrial Revolution it hardened into "steady labor."