Machiavelli, The Prince
"For this pattern of becoming overconfident at times of good fortune and inadequate at times of bad is a result of your habits of behavior and of your upbringing. If your education was foolish and weak, then you will be, too; if it was the opposite, then you will be the opposite. If you are brought up to have a decent understanding of the world, then you will be less inclined to get overexcited when things go well or get dismayed when things go badly. If this is true of an individual it is also true of a group of people living in the same state; they have the qualities that result from their society's habits of behavior"