If it had not been for the pernicious power of envy, men would not so have exalted vengeance above innocence and profit above justice... in these act… - Thucydides

(Athenian embassy:) [I]f through some legal decision of ours, or exercise of our imperial power, contrary to their own ideas of right, they suffer ever so little, they are not grateful for our moderation in leaving them so much, but are far more offended at their trifling loss than if we had from the first plundered them in the face of day, laying aside all thought of law. For then they would themselves have admitted that the weaker must give way to the stronger.

Mankind resent injustice more than violence, because the one seems to be an unfair advantage taken by an equal, the other is the irresistible force of a superior.

(Book 1 Chapter 77.3-4)

But his (Pericles’) successors were more on an equality with one another, and, each one struggling to be first himself, they were ready to sacrifice the whole conduct of affairs to the whims of the people.

Such weakness in a great and imperial city led to many errors, of which the greatest was the Sicilian expedition; not that the Athenians miscalculated their enemy's power, but they themselves, instead of consulting for the interests of the expedition which they had sent out, were occupied in intriguing against one another for the leadership of the democracy, and not only hampered the operations of the army, but became embroiled, for the first time, at home.

And yet after they had lost in the Sicilian expedition the greater part of their fleet and army, and were now distracted by revolution, still they held out three years not only against their former enemies, but against the Sicilians who had combined with them, and against most of their own allies who had risen in revolt. Even when Cyrus the son of the King joined in the war and supplied the Peloponnesian fleet with money, they continued to resist, and were at last overthrown, not by their enemies, but by themselves and their own internal dissensions.

(Book 2 Chapter 65.10-12)

Thus they toil on in trouble and danger all the days of their life, with little opportunity for enjoying, being ever engaged in getting: their only idea of a holiday is to do what the occasion demands, and to them laborious occupation is less of a misfortune than the peace of a quiet life. To describe their character in a word, one might truly say that they were born into the world to take no rest themselves and to give none to others.