"Nothing is more unpredictable than the mob, nothing more obscure than public opinion, nothing more deceptive than the whole political system."
That was said by Cicero. Cicero lived from 106 BC-43 BC, in ancient Rome. Something you could probably today put in the mouth of any random blogger, but they had their problems, and knew it, even back then.
For our purposes, we'll skip a few centuries past Cicero to 193 AD and one Didius Julianus. On March 28, 193, then-emperor Pertinax was assassinated in a soldiers' camp while trying to calm a mutiny. His assassins, having the benefit of no line of succession whatsoever, then announced that they would award the title of emperor to the highest bidder.
You see, they had a fucking valuable thing. You just don't give it away for nothing-- wait, what? Oh, these politicians today.
Okay. Emperor for sale. Pertinax's father-in-law and city prefect Titus Flavius Sulpicianus would have had a decent argument to the throne normally, but as it stood, he went ahead and started making offers. Meanwhile, Didius Julianus was sleeping at a banquet when his wife and daughter woke him up and filled him in on what was going on. Didius took off in a dead sprint for the camp, and when he found he couldn't gain entry, started shouting offers from the entrance. Titus offered 20,000 sesterces to every soldier- that being the currency of the time; Titus was essentially offering eight years' wages. Didius countered with 25,000. Auction over. Didius wins. Come on into the camp, New Emperor Person.
How did Rome in general react? They hated Didius on sight. Usually, they would cheer the new emperor. This time, they booed their lungs out, calling on multiple generals currently abroad to come home, oust this guy, and take the throne themselves.
Enter Septimius Severus, who simply declared himself emperor and made for Rome. (Another general, Clodius Albinus, would declare himself emperor as well, but Severus would get to Rome first.) Didius, being the corrupt office-buying unrespectable jerk he was and had been throughout his political career, found he didn't really have any allies to even begin to keep Severus out of Rome. People he sent as negotiators wound up defecting. He couldn't block Severus from entering, he sent assassins but they didn't do any good either.
And then he lost the soldiers from which he had bought the office. After some correspondence with Severus, they swapped themselves, proclaimed Severus emperor, and put out a hit on Didius. He would be assassinated on June 1, 193, "reigning" for a grand total of 66 days.
Just about the only person who didn't figure out why Didius Julianus was being killed off was Didius Julianus. Reportedly, his last words, as he was being assassinated, were "But what evil have I done? Whom have I killed?"