Cultivating virtues is practical for better consequences
Even though I'm a consequentialist, I think that intellectual, moral, and personal virtues are useful to practice and cultivate in our daily lives. It's unrealistic and tiring to derive all of your actions and decisions from the expected final outcomes. Especially when considering nuanced questions like whether you should tell a white-lie to your friend.
Even as someone who wants to have a positive impact, I don't want to do expected value calculations on whether to go to the movies with my friend because of the amount of good that money could do elsewhere. And if I start doing that, I'll just burn myself out and put much less effort into doing good altogether. (!*The best path is the one you'll stick to).
As humans we are lazy thinkers, so we tend to follow rules-of-thumb instead of always looking at the bigger picture. We need heuristics to lead us—like we do in all other areas of life—in making good decisions and being moral on a daily basis.
Instead of thinking about the consequences of every action, you can think about your goals and values very clearly for an hour, use those to give yourself some rules to follow or virtues to practice in your daily life, and now you don't need to worry as much about hard to predict long-term consequences. Because you come up with these values and virtues based on what you think will tend to have the best consequences, you'll do the right thing just by following these rules ~90% of the time, but with ~10% of the mental energy. This means that over the long-term, you are making it easier for yourself and more likely that you'll do the right thing. These virtues or values don't need to be perfect, eternal, or absolute to be useful.
It's simpler to never lie than to try to figure out the small portion of situations where it would be in everyone's best interest for you to do so.
It's simpler to be vegetarian than to only eat meat when you know it won't harm any more animals (e.g. it's about to be thrown out).
It's not worth spending time on these tiny decisions the way you might spend time planning your future career, but it is worth following your values to build this internal habit of making decisions in-line with your values. This is something that can make ?Doing good and feeling good overlap.
Further, doing what is right is often not a matter of figuring out what is best, but just doing it. When you are thrown into a challenging situation, do you have the patience, open-mindedness or kindness to choose the best action that you're resisting? Do you have the courage to tell the truth? Or the awareness to see your own biases? This is a measure of how habitual your virtues are. That is, how strong is your habit of sticking to your virtues, or heuristics that approximate them, when reacting to new situations. Figuring out the best course of action only matters if you're willing to take it.
TLDR:
Virtues are not eternal or perfect rules but just what tend to lead to good outcomes. They don't need to be grounded in some ultimate truth to be useful to consequentialists.
References:
Being curious is better than being smart. Being motivated and curious counts for more than being smart because it leads to action. Being smart will never deliver results on its own because it doesn’t get you to act. It is desire, not intelligence, that prompts behavior. As Naval Ravikant says, “The trick to doing anything is first cultivating a desire for it.” -- James Clear, Atomic Habits, pg. 261, loc. 3085-87