Again, it is possible to fail in many ways (for evil belongs to the class of the unlimited … and good to that of the limited), while to succeed is possible only in one way (for which reason also one is easy and the other difficult—to miss the mark easy, to hit it difficult); for these reasons also, then, excess and defect are characteristic of vice, and the mean of virtue; For men are good in but one way, but bad in many.

Book II, 1106.b28 - Nicomachean Ethics