“For we see men, in those activities that carry them towards the goal they all share, which is the acquisition of glory and riches, proceed differently. One acts with caution, while another is headstrong; one is violent, while another relies on skill; one is patient, while another is the opposite: and any one of them, despite their differences in their methods, may achieve his objective… This happens solely because of the character of the times, which either suits or is at odds with their way of proceeding… If the times and circumstances develop in such a way that his behavior is appropriate, he will flourish; but if the times and circumstances change, he will be destroyed for he will continue to behave in the same way…

I conclude, then, that… men flourish when their behavior suits the times and fail when they are out of step. I do think, however, that it is better to be headstrong than cautious, for fortune is a lady. It is necessary, if you want to master her, to beat and strike her. And one sees she more often submits to those who act boldly than those who proceed in a calculating fashion. Moreover, since she is a lady, she smiles on the young, for they are less cautious, more ruthless, and overcome her with their boldness.”

Niccolo Machiavelli, The Prince

In life you have to use 50% virtus and 50% luck because if a prince has only luck but doesn't use his intelligence to predict situations he will not remain as a prince for long. What he is saying is that luck needs to be conquered with boldness and calculating thinking needs to be used in the same measure. Cesare Borgia is the perfect example of a prince who used both fortune and Virtus.