One of the most well known saying in the Japanese language. It is a way of pointing out that everybody gets it wrong sometimes, that even cleverest among us, the most skilled, the most practiced they still make mistakes. It's an excellent way to keep overconfidence in check.
猫をかぶる ''To wear a cat on your head.''
良からぬことをたくらんでいる時、天使みたいに思わせ用途愛らしいふりをして無垢を装う、ということ。英語ではA wolf in sheep's clothing(羊の毛皮を被ったオオカミ)という言い回しがあります。
It is to pretend to be innocent, to feign sweetness in order to misled others into thinking that you are altogether angelic when in fact you may be up to no good. This is similar to the English saying, ''A wolf in sheep's clothing.''
People give advice with this saying to fussy young child. This is tender advice. Be careful about your language and behavior. Originally, the story goes back to the 15th century when the printing technology was invented. Mirror-reversed alphabets such as ''p'' and ''q'' were often mistyped. This saying came from the attention to workers that attention must be paid especially these two letters.