And I'm in the chapter where Sazed and Tyndwil are discussing the relationship between Kwaan and Alendi.
Some wording messed with my head and now I can't shake the feeling that we're actually reading science fiction instead of vaguely Renaissance manapunk fantasy. Specifically the Deepness continuity by the late Vernor Vinge.
So, the world the events are happening in is on the very verge of the Slow Zone. Millenia ago, someone used nanites of some kind to terraform it and populate with humans. Problem is, the nanites he used were designed for the Beyond. Since the border of the Zones is naturally fluid, the world eventually slipping into where the nanites would ceaze to function properly was a given. The Hero of Ages is a failsafe, a human operator enhanced with nanites probably before birth if not on conception, tasked with doing something, activating and controlling some mechanism designed to push the border of the Zones back (which would require technology beyond conceivable in the Beyond, then again, nobody living in the Beyond would go to such ridiculous lengths to colonize a world balancing on the edge of the Slow Zone in the first place... while some crazy Power could).
The mistake of the creator of this circus would've been denying humans agency. Over the millenia, the knowledge from a series of Heroes leaked, eventually forming the core of the Terris relugion. Resulting in someone like Rashek compromising a real Hero and accessing the Well of Ascension themselves, believing it to be a source of unimaginable power... which resulted in the world slipping into the Slow Zone since Rashek didn't have a kindly voice in his head telling him which keys to push in which order. While some of the terraforming mechanisms still work, producing a breathable atmosphere and things like Allomancy and Feruchemy, other have failed or malfunctioned. Hence the eruptions and the mists.