Faire d'une mouche un éléphant

Literally: To make an elephant out of a fly

Example: “Ce n'est qu'un petit retard, ne fais pas d'une mouche un éléphant.” — It's just a small delay; don't make a mountain out of a molehill.

English equivalent: To make a mountain out of a molehill

Origin: One of the oldest exaggerations on record. In the 2nd century, the Greek satirist Lucian ended his mock-serious Praise of the Fly with this phrase, presenting it as a saying already known, and Erasmus collected it in his Adages as elephantum ex musca facis, "you make an elephant out of a fly." The Académie française listed it in 1762, adding that it was said above all of a small fault blown far out of proportion. English prefers a molehill and a mountain.