expression
anyone can make a mistake; even experts slip up
Proverb literally meaning 'a kappa swept away by a river'; used to say that even an expert can fail in their own field.
彼はベテランのプログラマーなのに、簡単なバグを見逃した。まさに河童の川流れだね。
He's a veteran programmer, but he missed a simple bug. It's a perfect example of 'even a kappa can be swept away by a river.'
Similar proverb meaning 'even monkeys fall from trees'; both express that even experts make mistakes, but 河童の川流れ specifically uses the image of a water creature failing in water.
Another proverb with the same meaning, literally 'even Kobo Daishi makes brush mistakes'; more formal and literary.
From the folkloric creature kappa (河童), a water imp said to be an expert swimmer, being swept away in a river—its own domain—illustrating that even masters can fail.