also: せんりょのいっしつ
noun
a slip by a wise person; a mistake even the cautious make
A yojijukugo meaning that even a person of great wisdom and care can make a small oversight. Often used to excuse a minor error or to note that nobody is perfect.
彼の失敗は千慮一失というべきだろう。
His mistake should be called a mere slip by a wise person.
千慮一失で、ベテラン社員が簡単なミスをした。
Even a veteran employee made a simple mistake, a case of a wise man's oversight.
A proverb meaning 'even monkeys fall from trees,' used for anyone making a mistake despite expertise. 千慮一失 is more formal and specifically about a thoughtful person's rare slip.
Another proverb meaning 'even Kobo Daishi makes brush mistakes,' emphasizing that masters can err. 千慮一失 is a compact yojijukugo with a similar nuance.
From Chinese classical literature, combining 千慮 (a thousand considerations) and 一失 (one mistake). The phrase suggests that even after much thought, an error can occur.