万无一失
- Literal
- in ten thousand, not a single miss
- Figurative
- So safe that nothing can go wrong; said of foolproof plans or preparations, and also, with 以为, of what seemed certain but went wrong after all.
Where does 万无一失 come from?
It does not come from a specific anecdote: the idiom is built on a contrast of numbers. 万 is "ten thousand," a huge quantity, and 一失 "a single slip": in ten thousand tries, not one mistake. It is more categorical than 十拿九稳, which presents something as very likely, nine out of ten; 万无一失 leaves no margin at all. That is why it often comes with verbs like 确保 or 保证 when people talk about plans and preparations, and also in lines like 本以为万无一失, "we thought it was foolproof," when what seemed certain ends up going wrong.
How is 万无一失 used? Two examples
- 出门前我把护照检查了三遍，确保万无一失。
Before leaving I checked my passport three times to make absolutely sure nothing could go wrong.
- 我们以为方案万无一失，没想到上线第一天就出了问题。
We thought the plan was foolproof, yet it ran into trouble on the very first day after launch.
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