Virtù: that's the Italian word that Machiavelli keeps using when talking about strength or skill. But what exactly does it mean? Traditionally, something along the lines of having strength, skill, morality, and all that other good stuff. It also lets you master Fortune and bend it to your will so you never have "bad luck" again.
But Machiavelli has taken virtù and run with it. Your strength could be cruelty, or your skill could be lying. That doesn't seem quite right, does it? Somehow, Machiavelli seems to define the word differently for each ruler. Look at all the ways that the word has been translated: talent, mental and physical qualities, ingenuity (a fave with Machiavelli scholars), risk-taking, positive qualities, brilliance, ability, determination, strong character—and the list could go on. So maybe virtù is just anything that you need to win.
In The Prince, virtù is whatever you want it to be.
According to Machiavelli, strength and skill matter more than luck in determining a ruler's success.