When Aristotle applies his doctrine of the mean to the virtue of courage, he has a problem. The epitome of courage for the Greek polis is the courage of the heavy infantry hoplite solider, and a mean between rashness and cowardice doesn't cut it. The hoplite must have the courage to surrender his life, no matter what. That's just how the shock battle of heavy infantry with shields and spears works.
But once we get away from courage then the full meaning of Aristotle's virtue theory can work. A person with practical wisdom, equipped to live a life of eudaimonia, has learned to live a life of the moderate mean in between excess and defect, in the right way at the right time for the right reason. And right action is directed by the ability to think the right thoughts. Action is preceded by thought, and the temperate man "is so called because he is not pained at the absence of what is pleasant and at his abstinence from it."
The man of practical wisdom knows that "if appetites are stong and violent" they can overcome moderation, so he cultivates moderation and develops the habit of moderation. He knows that the only way to live a happy life is to make sure that "the appetitive element should live according to rational principle" and not the other way around.
Once you get away from the moderate rational principle then you are in danger of succumbing to the appetitive element: self-indulgence. There may be some that are so insensitive to the urges of pleasure, but they "are hardly found," says Aristotle. So the question of temperance is largely a question of the regulation of self-indulgence, the appetitive urge. And that requires a life-long devotion to a life of moderate rational principle, the practical wisdom of living, doing the right thing for the right reason in the right way at the right time.
But it's worth it, because it all leads to eudaimonia.