Explain the relationship between Fortuna and Virtus in Ceasar

In Ceasar's speech after the battle of Dyrrhachium (during the 49 BC - 45 BC Civil War), a battle which supposedly Pompeius won, but with conspicuous casualties on both sides, we see magnifically exeplified the oratio post-cladem. In this specific oratio, Ceasar invited his soldiers to not feel disheartened, because Fortuna ("luck") is on his side. Fortuna can be construed or helped by one's intelligence and sense of moderation, he explains. This is why Virtus and Fortuna are complementary concepts; the first prepares the ground for the advent of the second and when the latter should fail, a man's virtuous action and determination can help him achieve (and bring upon himself) res fortunae (happy events, good things).