Is it Really Darkest Just Before the Dawn?

I’m back to inviting readers to submit quotations whose origins they want me to try to trace, using my book, The Yale Book of Quotations, and my more recent researches.
Georgia asked:

“where does the saying ‘the world is your oyster’ come from?”

According to the Oxford English Dictionary, this is an allusion to “the possibility of finding a pearl in an oyster” and means “one is in a position to profit from the opportunities that life, or a particular situation, may offer.”  The earliest citation for the expression given by the OED is from Shakespeare’s Merry Wives of Windsor: “Why then the world’s mine Oyster, which I, with sword will open.”

Photo: Li-Ji

Josh asked:

“I always get annoyed by people who say, ‘It’s always darkest just before the dawn,’ usually said to cheer somebody up who’s down on their luck with hope of better times.  I’d prefer people either offer a unique thought or something that makes scientific sense. Where did this horrible quote come from?”

A great question, Josh, one that has long vexed me. We all understand the metaphorical point of this proverb, but proverbial metaphors usually play off of commonly accepted realities.  It’s just not a reality that it’s always darkest just before the dawn.  According to The Yale Book of Quotations, the earliest known version of the saying is in Thomas Fuller‘s, A Pisgah Sight of Palestine (1650) (“It is always darkest just before the Day dawneth”), but that doesn’t help us with the puzzing question of why it arose.  Can any reader suggest an explanation?
Do any readers have any other quotations whose origins they would like me to attempt to trace?