Explanation: Of these three historians of the Roman Empire during its height, Tacitus, Cassius Dio, and Suetonius, Suetonius is sometimes considered the... least reliable of the three.

Tacitus, admittedly, is heavily moralistic in his writing, attempting to demonstrate narrative lessons in-line with his view of virtue. Cassius Dio is a Senatorial partisan and political animal, and a Greek by upbringing and cultural inclinations, and that deeply colors his narratives. But both are considered generally reliable, and not too eager to pass-on unsubstantiated details (Dio's occasional partisanship aside, such as on Elagabalus).

But Suetonius is... very Roman, in that he is enamored with rumor and scandal. Suetonius certainly passes on all the tabloid gossip one could wish for - and while he generally admits when something is rumor rather than fact, he relays it with such enthusiasm and detail that one could be forgiven for misremembering every piece of slander in De vita Caesarum as trivia rather than hearsay!