A: I should send the client the final version of the file, but there are so many that it’s hard to tell. Which file is the final version? I just don’t want to send the wrong one by accident.
B: The one labelled ‘FINAL_APPROVED’. It’s impossible to mistake it, so you’ll be fine.
A: Got it. Thanks for clarifying. I feel more confident now.
B: No problem. Let me know if anything comes up.
In this situation, what should you say ‘it’s impossible to mistake it’ in Japanese?
Casual
B：「最終版」と書いてあるファイルです。間違えようがないので大丈夫ですよ。
Note: This is not a word-for-word translation.
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A word-for-word translation
B：「最終版」と書いてあるファイルです。間違えることはあり得ないので大丈夫です。
Although 間違えようがない and 間違えることはあり得ない have the same meaning, they create a different impression.
When you say 間違えることはあり得ない, I think it may sound a bit strong and cause offence in some cases.
For example, they may feel that you perhaps consider them a bit of a fool because they don’t know the obvious thing, which makes them more stressed as they feel they must not fail.
Using 間違えようがない allows to indicate that it’s really easy to tell and you can give relief to them who are anxious.
Kotoba no Hibiki 