expression
anyone can make a mistake; even experts slip up
Proverb literally meaning 'even Kōbō Daishi's brush makes mistakes,' used to console someone who has made an error by noting that even the greatest masters are not perfect.
失敗しても気にしないで。弘法にも筆の誤りというから。
Don't worry about the mistake. As they say, even Homer sometimes nods.