Literal meaning
trouble (患) — difficulty (难) — of (之) — friend (交)
Origin
A traditional four-character phrase rooted in the broader Confucian observation that 患难见真情 — "hardship reveals true feeling." Only adversity tests friendship; everyone shows up to the celebration, but the friend who shows up at 2 a.m. when your life is falling apart is the one that matters. The phrase has been a stock expression in Chinese letters and biographies for centuries.
Examples
Usage & nuances
Warm, sincere register. Used to mark a friendship's real depth — wouldn't apply to casual acquaintances. Common in biographies, eulogies, and how people describe their oldest friends.
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