Tacitus' claim that history should inspire good deeds and deter bad ones (Annals 3.65) should be taken seriously: his exempla are supposed to help his readers think through their own moral difficulties. This approach to history is found in historians with clear connections to Stoicism, and in Stoic philosophers like Seneca. It is no coincidence that Tacitus is particularly interested in the behavior of Stoics like Thrasea Paetus, Barea Soranus, and Seneca himself. They, and even non-Stoic characters like Epicharis and Petronius, exemplify the behavior necessary if Roman freedom was to survive the monarchy.
"Tacitus, Stoic "Exempla", And The "Praecipuum Munus Annalium"".