Around the web, you will find the following:
Cornelius Tacitus: He had a certain frankness and generosity, qualities indeed which turn to a mans ruin, unless tempered with discretion.
The thought was striking, as indeed it should strike anyone who is fairly open, like myself. But is it Tacitus?
Well it is! It is in fact from the Histories, book 3, chapter 86, as translated by A.J.Church and W.J.Brodribb (London, 1873 in this case, p.140.) It is a description of the character of Vitellius!
I had not encountered this, but am glad to known the details if I do in future – thanks!
I don’t think he quotes Tacitus, but it strikes me as fitting in interestingly with the analysis by St. Aelred of Rievaulx in “On Spiritual Friendship”, which attends to Cicero (and, I think I recall, other non-Christian classical authors).