A proverb meaning 'even experts make mistakes' (literally: even Kōbō Daishi makes mistakes with his brush).
彼はプロの選手だけどミスをする。弘法にも筆の誤りだね。
He's a pro player but he makes mistakes — even experts slip up sometimes.
完璧を期待しすぎるのはよくない。弘法にも筆の誤りというでしょう。
It's not good to expect perfection. As the saying goes, even experts make mistakes.
上司がミスをしたとき、部下が『弘法にも筆の誤りですね』と言って場を和ませた。
When the boss made a mistake, an employee said 'even experts make mistakes' to lighten the mood.