The origins of this ancient ritual are 'lost in the mists of time'.
My glasses 'misted' [='fogged'] 'up' when I came in from the cold.
Her eyes 'misted over' as she thought of her old friends.
(..) Very lucky we find you. Nice Hobbit. It's a bog. He's led us into a swamp. A swamp, yes, yes. Come, master. We will take you on safe paths through the mist. Come, Hobbits! Come! We go quickly. I found it. I did. The way through the marshes. Orcs don't use it. Orcs don't know it. (..)2002 The Lord of the Rings: The Two Towers