it's a comical way to say "keep going" or "push through" or whatever. its supposed to be an encouraging quote and usually serves its purpose, also making that personsmile
"dude i've been so sad. i can't believe he left me for that other girl"
"hey, keep your head up princess, your tiara is falling"
A sly way of calling a girl as perfect and graceful as a princess when cheering her up. An encouragement to just keep standing proud.
Girl: Ugh, literally nothing is going right today. I fell flat on my face in the audition, and my best friend is not talking to me anymore. I just feel so awful.
You: Oh that's awful! You deserve way better than that. Just Keep Your Head Up Princess, Your Tiara Is Falling
When some resigns or retires from a job, they are on "eternity leave". This can also refer to someone who has passed away, especially someone who worked somewhere for a long time, retired/resigned, then passed away later.
Oh I'm sorry, you didn't know that Kelly is on eternity leave? She resigned and moved to Hawaii!
With regrets I would like to inform you that my boss is officially on eternity leave. I will never see or hear them again. Ever.