War is a violent teacher, - Thucydides

Revolution thus ran its course from city to city, and the places which it arrived at last, from having heard what had been done before, carried to a still greater excess the refinement of their inventions, as manifested in the cunning of their enterprises and the atrocity of their reprisals. Words had to change their ordinary meaning and to take that which was now given them. Reckless audacity came to be considered the courage of a loyal supporter; prudent hesitation, specious cowardice; moderation was held to be a cloak for unmanliness; ability to see all sides of a question incapacity to act on any. Frantic violence became the attribute of manliness; cautious plotting a justifiable means of self-defense. The advocate of extreme measures was always trustworthy; his opponent a man to be suspected. To succeed in a plot was to have a shrewd head, to divine a plot still shrewder; but to try to provide against having to do either was to break up your party and to be afraid of your adversaries.

(Corinthian:) And if we allow ourselves to be divided or are not united against them (Athenians) heart and soul — the whole confederacy and every nation and city in it — they will easily overpower us. It may seem a hard saying, but you may be sure that defeat means nothing but downright slavery,

and the bare mention of such a possibility is a disgrace to the Peloponnese: — shall so many states suffer at the hands of one? Men will say, some that we deserve our fate, others that we are too cowardly to resist: and we shall seem a degenerate race. For our fathers were the liberators of Hellas,but we cannot secure even our own liberty; and while we make a point of overthrowing the rule of a single man in this or that city, we allow a city which is a tyrant to be set up in the midst of us.

(Book 1 Chapter 122.2-3)

Themistocles was a man whose natural force was unmistakable; this was the quality for which he was distinguished above all other men;from his own native acuteness, and without any study either before or at the time, he was the ablest judge of the course to be pursued in a sudden emergency,and could best divine what was likely to happen in the remotest future. Whatever he had in hand he had the power of explaining to others, and even where he had no experience he was quite competent to form a sufficient judgment;no one could foresee with equal clearness the good or evil event which was hidden in the future.In a word, Themistocles, by natural power of mind and with the least preparation, was of all men the best able to extemporise the right thing to be done.

(Book 1 Chapter 138.3)