The peak civilizations of the first eight Epochs, which arose respectively, also vary in strength.
The responsibilities they bore differed greatly.
Some civilizations left behind a great inheritance for posterity. Others squandered much of it.
The older peak civilizations weren't necessarily stronger. Among these civilizations, many fell or fled.
Nor are the newer ones necessarily stronger.
Take the peak civilization of the Eighth Epoch, for instance—it wasn't particularly impressive... Its responsibilities were too few, likely shortening the lifespan of the Ninth Epoch.
This is inevitable. How many civilizations in this world are willing to fight against Epoch Disasters? If I can protect myself, why should others' lives and deaths concern me?
Earth lasting into the Ninth Epoch has been the result of many twists of fate.
"Peak civilization? Humph, overthinking it! By then, we'll already be dead!"
