First, let's be aware of willpower as a resource. Willpower is the ability to make decisions, to follow through with them, to stick to the course of action no matter what. Willpower is what we use to master our emotions. Without it, we can do nothing.
Second, let's define what emotions are. As far as we can tell they're mental states that predispose you to certain actions. Anger makes you more likely to fight, fear makes you more likely to flee, and so on. There are many different emotions but the complicated ones are just combinations of a handful of basic feelings: fear, pain, anger, and pleasure. Disgust, for example, is a mix of fear and anger. We are afraid of becoming infected by whatever it is. At the same time we are angry to be confronted by such an unclean thing. Nostalgia, on the other hand, is a mix of pleasure and pain. It gives us pleasure to think about the good times. It hurts to know that those times are gone.
If we had to reduce the number of emotions further, then it boils down to two feelings: pain and pleasure. Pain drives us to avoid things while pleasure drives us to toward things. Fear is a kind of pain and so is anger. The first one pushes us to flee from danger while the other overwhelms the first one and motivates us to destroy the danger.
Now, knowing all that, we can guess gaining a virtue would involve enhancing one's willpower, while losing a virtue would involve doing the opposite. Becoming more patient, for instance, would require an extra helping of willpower in order not to do anything hasty. It may also involve either the blunting or the sharpening of certain emotions. Dial down on the anger and we become more able to deal with our temper. Dialing up the happiness and we become more easygoing.
