forti et fideli nihil difficile (L) Nothing is difficult to the brave and faithful.

fortiter in re, suaviter in modo (L) forcibly in deed, gentle in manner.

fortuna favet fatuis [fortibus] (L) Fortune favors fools [the brave].

fortuna vitrea est; tum, cum splendet, frangitur (L) Fortune is glass; just when it becomes bright, it is broken.　― Publilius Syrus, Sententiae 284.

froides mains, chaud amour [chaudes amours] (F) Cold hands (is the sign of) warm heart(s).