Aristotle, Eudemian Ethics

[1234b] [1] because the mean does not occur in combination with either extreme, whereas the extremes often do occur in combination with one another, and sometimes the same men are venturesome cowards, or extravagant in some things and illiberal in others, and in general not uniform in a bad way— for when men lack uniformity in a good way, this results in men of the middle characters, since the mean contains both extremes.

The opposition existing between the mean and the extremes does not seem to be the same in the case of both the extremes, but sometimes the greater opposition is by way of excess, sometimes by way of deficiency. The causes of this are partly the two first mentioned,¹ rarity (for example, the rarity of people insensitive to pleasant things) and the fact that the error to which we are more prone seems more opposite to the mean, and thirdly the fact that the extreme that more resembles the mean seems less opposite to it, as is the case with daring in relation to boldness² and extravagance in relation to liberality. We have therefore sufficiently discussed the other praiseworthy virtues, and must now speak about Justice.³