The legends of ancient Unova claim that the lightning bolts of heaven, or in some tellings Thundurus (as distinguished from the far smaller shocks produced by pokemon such as Emolga) do not exclusively fall from the heavens; they can race just as fast and dangerously across the land, and when they do so they are given the name Zebstrika. The line between the two phenomena has long been blurred in this cosmology. Lightning is portrayed in art exclusively as white and ringed in black, not yellow as in much of the world, and falls in patterns resembling a Zebstrika's horn and mane.
The corollary of this belief is that a Blitzle's evolution, despite the relatively minor morphological differences compared to those of many other pokemon, is treated as a profound and tragic transformation; Zebstrika are not mature Blitzle, but a terrifying force of nature which had somehow possessed and transformed a living pokemon. And to be sure, Zebstrika's behavior gives credence to this idea; they race long distances across Unova in pursuit only of satisfying their curiosity, and they discharge powerful electrical shocks in all directions, not exclusively at their enemies.
Modern science has offered a less legendary explanation for the Zebstrika. It has won credence among many trainers, who by considering it a simple evolution explain away the fact that their evolved Blitzle still remember them and treat them with some fondness and obedience, although never quite as much as before, and avoid the guilt that would come with their pokemon losing their soul to a lightning bolt. Others adhere to traditional beliefs, some out of piety, others because they love the idea of being able to command and ride upon not a common pokemon, but a deadly force of nature thrown by Thundurus itself.