Question

Keep your chin up and I hope you break a leg! It only happens once in a blue moon. What does this idiomatic phrase actually mean?

Look upwards and keep smiling. It only happens once every month.
Stay positive and I wish you good luck! It hardly ever happens.
Stop talking and I hope you have lots of fun! It only happens once every year.
Don’t stare at the ground, I wish you would fall over! It happens all the time.

Answer 1

Pikachu! Your answer ^_^ 
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This is very confusing phrase though it means

Look upwards and keep smiling. It only happens once every month

Keep your chin up means to keep smile on your face. Being happy even in toughest situations

To break a leg means to wish someone good luck

Once in a blue moon means occurring very rarely

So its full definition is when someone is going for doing something really good and he is afraid that he won't be able to do so then we wish him keep your chin up (be happy), to break a leg (good luck) and happen once in a blue moon (occur rarely)
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Pikachu! ^_~
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