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text from Terry Pratchett; art by Higgs who's tumblr i've linked
i can't rember which book this is from -- i wanna say it's Men at Arms but it could even be Guards Guards. Higgs seems to think it's Night Watch, but I'm pretty sure it happened before that...
in the post here
It's a real phenomena, but passage is couched in the perspective of a fictional character in a fictional world. This isn't "the only reason", it's just one that stands out to the character.
to complicate things even more the setting is late medieval semi victorian