An Idiom a Day
don't teach your grandmother to suck eggs
217) don't teach your grandmother to suck eggs — no vulguis ensenyar una cosa a algú que en sap més que tu (ex.: I don't want to teach my grandmother to suck eggs, but aren't you supposed to back up your work? = No vull ensenyar-te el que saps millor que jo, però no has de fer una còpia de seguretat?).