Niccolò Machiavelli
Discourses on the First Decade of Titus Livius (Chap. 1.42)
How easily Men become corrupted.

In this matter of the decemvirate we may likewise note the ease wherewith men become corrupted, and how completely, although born good and well brought up, they change their nature. For we see how favourably disposed the youths whom Appius gathered round him became towards his tyranny, in return for the trifling benefits which they drew from it; and how Quintus Fabius, one of the second decemvirate and a most worthy man, blinded by a little ambition, and misled by the evil counsels of Appius, abandoning his fair fame, betook himself to most unworthy courses, and grew like his master.

Careful consideration of this should make those who frame laws for commonwealths and kingdoms more alive to the necessity of placing restraints on men's evil appetites, and depriving them of all hope of doing wrong with impunity.