A proverb meaning that even experts sometimes make mistakes; nobody is perfect.
彼はこの道の権威だけど、弘法も筆の誤りでたまに間違えるよ。
He's an authority in this field, but even experts make mistakes sometimes.
ミスして落ち込まないで。弘法も筆の誤りと言うじゃないか。
Don't get down about the mistake. After all, even experts slip up.
プロの選手でもミスはある。弘法も筆の誤りだね。
Even professional players make errors. It's the 'even Homer sometimes nods' situation.