Aristotle said that virtues are means between extremes. He is not saying that everyone should strive to be mediocre and emotionally tepid in everything that they do. The mean is relative to each situation. So sometimes you are following the mean by being distraught (like when a loved one passes away), while other times you are following the mean by being joyful (like when your child is born). The person of virtue consistently responds with the “mean” reaction in a particular sphere of experience. In the sphere of experience relating to dangers, courage is the mean between “rashness” (a tendency to not fear what is fearful, or to rush in to face foolish dangers) and “cowardice” (a tendency to fear too much, or to give in to fear too easily).
This account is not unproblematic. And it certainly needs to be supplemented to be fully adequate. (Aristotle and later Aristotelians have done some of that supplementing, but not all that is needed.) But it is often a good starting point when thinking about virtues and vices.
Consider two extremes: naivete and cynicism. I’m not sure we have a generally accepted name for the mean state between these extremes. “Realism” is tempting, but that’s already a technical term in philosophy. Perhaps “reflectiveness”? Although they are opposite extremes, naivete and cynicism are very similar. Both the naive and the cynical assume that their prejudgments are accurate; each is disposed to a particular kind of prejudgment of the motives of others; neither is sufficiently responsive to evidence that their prejudgments are wrong. The naive person assumes that person A is motivated by kindness and integrity. He will cling to this assumption in the face of behavior from A that makes this incredibly implausible. The cynical person assumes that person B is motivated by selfishness. He will attribute to B the most unusual beliefs, for which there is no evidence, and invent complicated variations of self-interest, in order to maintain his presumptions.
Ironically, both the cynical and the naive person tend to assume that humans are rational. They are blind to the all-too-common cases of the basically kind person taking exactly the wrong means to help others, or the self-interested person acting self-destructively.