In the Storytelling System, Virtues and Vices are intrinsic elements of a person's identity, and both equally reinforce a sense of self, whether they like to admit it or not. They act as anchors to a character's personality.
Every character starts with one defining Virtue and one defining Vice. While Virtue and Vice may clearly reflect the character's background and concept, they can contrast with his outward nature and create sources of conflict within himself. However, when a character's actions in difficult situations reflect his particular Virtue or Vice, he reinforces his fundamental sense of self (however it should be noted that everyday expressions of, say, Faith or Pride are not enough to reaffirm a character's determination or sense of self).
Fulfilling a Virtue is more rewarding than fulfilling a Vice for two reasons. One, it is inherently challenging to accomplish a surpassing act of goodness in a world that's rife with selfishness and aggression. Doing so demands sacrifice and perseverance. Two, the temptation to indulge base inclinations and desires is constant and often means taking the path of least resistance, which precludes doing the greater good. Fulfilling Vices therefore offers small rewards that are easy to come by.
Virtues are means that grant a character a great sense of self-actualization, but which they are often tempted to ignore. A character can have "ambitious" as a virtue if following their ambitions is what makes them more fulfilled or "generous" if offering help to others is their central mission.
Vices instead are short-term comfort and a distraction from the world. Often, they are means to distract oneself from problems. A character can have "ambitious" as a vice if advancement is all that they care for, or "generous" if they are moved to acts of compassion that they consider a sign of weakness on their own part.
In the 1st Edition of the Chronicles of Darkness, Virtues and Vices were drawn exclusively from the Seven Deadly Sins and the Seven Heavenly Virtues and were shared by mortals and supernaturals alike. 2nd Edition allows for the construction of personalized virtues or vices for humans, as well as introducing multiple alternate character elements for inhuman supernatural beings.