Everybody loves a thing more if it has cost him trouble: for instance those who have made money love money more than those who have inherited it.
Aristotle[the virtues] cannot exist without Prudence. A proof of this is that everyone, even at the present day, in defining Virtue, after saying what disposition it is [i.e. moral virtue] and specifying the things with which it is concerned, adds that it is a disposition determined by the right principle; and the right principle is the principle determined by Prudence.
Aristotle