河童の川流れ (かっぱのかわながれ): anyone can make a mistake; even Homer sometimes nods

anyone can make a mistake; even Homer sometimes nods

The kappa is a river spirit that lives in the water, and even it gets swept away. Reach for it when a genuine specialist slips, where 猿も木から落ちる would do for anyone merely competent.

A Japanese proverb (ことわざ)