These words have been uttered by many in one form or another. I came across them again in a letter of Pliny the Younger describing for the Roman historian Tacitus the brave actions of his uncle, Pliny the Elder, in the face of the eruption of Mt. Vesuvius on August 24, 79 A.D. The uncle died during the eruption.
Here is the saying in Latin: "Fortes fortuna iuvat" (classical Latin uses "i" as a letter "j").
The Loeb translator suggests that Pliny the Elder was quoting Terence's words found in his play Phormio (Act I, scene iv, line 203).
You can find the same saying in Vergil and also uttered by other historical figures with similar or different words. Caesar was a famous believer in the role of the goddess Fortuna which nevertheless called for individuals to take the bull by the horns in order to benefit from fortune. (See link.)
This ancient wisdom seems trite, but it is really quite profound.
Regardless of the limits imposed by our circumstance, we have a margin of action. In the Judeo-Christian tradition, we call it free will. Even the most avowed determinist will live as if he or she has that free margin of action. Look at what people do, not at what they say. Within limits, we are indeed free.
Boldness is a recommendation for engaging that margin of freedom, hopefully after we have prudently scouted the terrain.
(Image of Caesar at the Rubicon in public domain)