Aristotle next takes up the virtue of gentleness. It's the mean to anger, which means that it's a deficiency of anger.
Again, we have a language problem: neither the true deficiency of anger (i.e. not gentleness) nor the excess have proper names. He does call the excess "irascibility."
A gentle person may also get angry, but only when it's appropriate to do so.
It is not a virtue to hold your anger back when you should be angry, even though it's generally good to keep a handle on your temper.
If you are irascible, don't despair. You still tend to cool out pretty quickly, so there's no grudge-bearing or vengeance-seeking.
But if you're both irascible and grudge-bearing, you run the risk of becoming bitter.
A bitter person will seek a place to vent their displeasure, but likely never through a mediator since they don't like to talk about things. They generally go in for revenge.
Harshness is another form of excess on the anger spectrum. No remediation for this guy, either; he can only find relief in retaliation.
The difficulty with anger? Humans are inclined to vengeful behavior—and it can be hard to suss out how angry we should be in any given situation.
And the thing is, sometimes we praise people who are a little on the angry side (i.e. as "masculine" or "assertive").
Aristotle wants to be consistent, so he urges us to drive right down the middle of this road: not too angry, but not too passive, either.