The influences of Rula and Sorna from Multor, as well as the whispering of Nital led many gods to see the strengthening of the ley-network as crucial to the protection of Creation. Otherwordly terrors had plagued Creation for centuries, and so barriers to such incursions were seen as necessary.
The Obscuring Mists are one of these barriers, perhaps the most prevalent and deadly of them too. Anyone seeking to traverse between Creation and another plane of existence without the use of some sort of portal must brave the Mists. Oftentimes the Mists will confuse and misdirect those wandering the space between planes, bringing them right back to their starting point. Other lose their way forever, becoming permanent residents of this dreary place. The average mortal lost in the Mists do not last very long; horrors coming from Multor fall prey to the Mists as well and prowl the shadows.
Divine beings, as well as mages who have traversed the Mists often enough to learn its complex layout and nature might stand a better chance at making a safe journey. The elder dragons and Avashai of Tar Vash'eth have been known to lead large numbers of mortals through the Mists to their hidden city.