Explanation: The Roman Emperor Diocletian, after becoming Emperor, demanded that everyone treat him as a living god. This, while having precedent in Hellenic parts of the Empire, and in Persia, was deeply abnormal and offensive to traditional Roman norms, which regarded the Emperor as a magistrate appointed by the Senate and People, merely 'First Amongst Equals' and 'First Citizen'.
Traditional incarnations of the Roman 'Imperial Cult' were deeply linked with traditional Roman religion, in which one would pay religious respects to one's household's ancestors (the manes et lares). As the Emperor was seen as 'Pater Patriae', Father of the Fatherland, paying respect to dead Emperors was seen as wholly natural and appropriate, the way one might respect their actual father or grandfather - to pay such respect to living Emperors, unthinkable and sacrilegious.
However, the Hellenic eastern half of the Empire had essentially always worshipped Emperors (and sometimes lesser officials as well) as living gods, even though such practice did not previously receive recognition from the Imperial apparatus. As such, Diocletian's delusions of godhood were not a major change for a good proportion of the Imperial population.