'Shì bù yí chí' is a classical four-character idiom meaning 'the matter brooks no delay' or 'there's no time to lose.' Literally, it breaks down as: 事 (shì) = 'matter' or 'affair'; 不 (bù) = 'not'; 宜 (yí) = 'appropriate' or 'advisable'; 迟 (chí) = 'to delay' or 'to postpone.' So the phrase conveys that delaying this matter would be inappropriate — in other words, immediate action is required. It carries a tone of urgency and seriousness, often used in formal advice, warnings, or decisive recommendations.

This idiom appears frequently in written Chinese — such as official notices, news reports, or persuasive speeches — and occasionally in spoken language when emphasizing gravity and timeliness. It’s not used for trivial matters; rather, it signals that consequences may follow if action is postponed. Though grammatically an idiomatic noun phrase, it functions adverbially in sentences, typically preceding a verb clause (e.g., '事不宜迟，我们马上出发。'). Its roots lie in classical Chinese, lending it a refined, authoritative register.