“The fate of those of their neighbours who had already rebelled and had been subdued was no lesson to them; their own prosperity could not dissuade them from affronting danger; but blindly confident in the future, and full of hopes beyond their power though not beyond their ambition, they declared war and made their decision to prefer might to right, their attack being determined not by provocation but by the moment which seemed propitious. The truth is that great good fortune coming suddenly and unexpectedly tends to make a people insolent; in most cases it is safer for mankind to have success in reason than out of reason; and it is easier for them, one may say, to stave off adversity than to preserve prosperity.”
Book III, 3.39-[3]
History of the Peloponnesian War, Book III
Help us to complete the source, original and additional information
Thucydides 76
Greek historian and Athenian generalRelated quotes

“The truth is really an ambition which is beyond us.”
As quoted in International Herald Tribune (12 March 1990)
Asia and Western Dominance: a survey of the Vasco Da Gama epoch of Asian history, 1498–1945

1860s, First Inaugural Address (1861)

“Prosperity proves men to be fortunate, while it is adversity which makes them great.”
Secunda felices, adversa magnos probent.
XXXI.
Panegyricus

Letter to Robert Baldwin Hayward (1892), as quoted in Energy and Empire : A Biographical Study of Lord Kelvin (1989) by Crosbie Smith and M. Norton Wise