How do you translate "The sun must set to rise"?
A line from a Coldplay song called "Paradise", here it is in context:
"And so lying the stormy skies, she said ohhhhh, I know the sun must set to rise"
It basically means that you must persevere through dark times, in order to get back to good times :)

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To keep the meaning, there is an expression that says "Il y a de la lumière au bout du tunnel" (there is light at the end of the tunnel) but if you want a litteral translation, it would be "je sais que le soleil doit se coucher pour se relever"

I just thought of another expression: "Quand on touche le fond, on ne peut que remonter " (when you touch the bottom you can only go up).

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I think you can translate "I know the sun must set to rise" by "Je sais que le soleil se lèvera".
Possibly "Je sais que le soleil doit se lever" but it sounds worst.