(Via Philosophical Dictionary)
A general must seek to find courage, the mean between cowardice and foolhardiness, in order to gain honor. . . . A person who seeks pleasure through eating must find the mean between being a glutton and starving. . . . A person who seeks honor through knowledge must find the mean between ignorance and seeking knowledge to excess.
We must not understand Aristotle to mean that virtue lies exactly at the centre of two vices. Aristotle only means that virtue is in between the two vices. Different degrees are needed for different situations. Knowing exactly what is appropriate in a given situation is difficult and that is why we need a long moral training. For example, being very angry at the fact that your wife is murdered is appropriate even though the state is closer to extreme anger (a vice) than it is to indifference (a vice). In that case, it is right for the virtuous man to be angry. However, if some water has been spilt in the garden by accident then the virtuous response is much closer to indifference.