Literal meaning
hear (闻) — one (一) — know (知) — ten (十)
Origin
Analects (《论语·公冶长》). Confucius is comparing his two disciples Zigong (子贡) and Yan Hui (颜回). Zigong demurs: 回也闻一以知十，赐也闻一以知二 — "Yan Hui hears one and knows ten; I [Zigong] hear one and know only two." The phrase has come down through 2,500 years as the standard way to mark someone as exceptionally fast at inferring the bigger pattern from a small example.
Examples
Usage & nuances
Genuine praise — not used sarcastically. Reaches naturally across spoken and written registers. Mild risk of overuse on children; reserve for someone whose inference is actually impressive rather than as a default compliment.
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