To be nice is not to be good, to be good is to stand for what is good.
Being nice is polite, wanting to be being liked, and sacrificing the good to get along, despite knowing better.
Sure, you can be nice and kind up to a point or be politically astute up to a point, but a whole person (an authentic, emotionally secure, resilient individual) will cease polite agreement and take a stand for what is good.