Laudator Temporis Acti

Ronald Syme, "How Gibbon Came to History," in his Roman Papers, III (Oxford: Clarendon Press, 1984), pp. 969-976 (at 971):

The classic historians almost conform to a pattern: the man of mature years, after a political life, turning to the writing of history, often as a continuation of that life, and indeed, some of them having been condemned to leave their own country. Observe of the classic Greek historians what exile did for Herodotus, Thucydides, Xenophon, and Polybius. Can each or all of them be properly conceived without the hard lessons of exile?

As for the Romans, Sallust turns to history after the failure of a political career. Tacitus, on the contrary, had been highly successful, but he adopts an attitude of estrangement—not indeed that he was estranged from contemporary society, I fancy. Both Sallust and Tacitus are commonly described as pessimistic historians. Yet, had these men been really pessimistic, they would have given themselves over to drink or dissipation, they would have sought the consolations of religion or philosophy. Instead, they find that there is some work to be done: that is to say, the writing of history.