Kǎoshì nándù chāochū yùqī, kǎoshēng men jiàokǔbùdié.
The exam was harder than expected and the test-takers couldn't stop groaning about it.
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history
Attested in the Song-dynasty work 《大宋宣和遗事》: 徽宗叫苦不迭, 'Emperor Huizong cried out in distress without pause, then suddenly woke up on his bed.'
memory
不迭 is an older compound meaning 'unable to stop or keep up' (迭 = to alternate; 不迭 = can't catch up, i.e. non-stop). So literally: 'crying out in distress, can't stop'.