Niccolò Machiavelli
Discourses on the First Decade of Titus Livius (Chap. 1.41)
That it is unwise to pass at a bound from leniency to severity, or to a haughty bearing from a humble.

Among the crafty devices used by Appius to aid him in maintaining his authority, this, of suddenly passing from one character to the other extreme, was of no small prejudice to him. For his fraud in pretending to the commons to be well disposed towards them, was happily contrived; as were also the means he took to bring about the reappointment of the decemvirate. Most skilful, too, was his audacity in nominating himself contrary to the expectation of the nobles, and in proposing colleagues on whom he could depend to carry out his ends. But, as I have said already, it was not happily contrived that, after doing all this, he should suddenly turn round, and from being the friend, reveal himself the enemy of the people; haughty instead of humane; cruel instead of kindly; and make this change so rapidly as to leave himself no shadow of excuse, but compel all to recognize the doubleness of his nature. For he who has once seemed good, should he afterwards choose, for his own ends, to become bad, ought to change by slow degrees, and as opportunity serves; so that before his altered nature strip him of old favour, he may have gained for himself an equal share of new, and thus his influence suffer no diminution. For otherwise, being at once unmasked and friendless, he is undone: