This is a riddle from one of my favorite books: Harry Potter and the Deathly Hallows from Luna Lovegood.
“Which came first, the phoenix or the flame?’
‘Hmm . . . What do you think, Harry?’ said Luna, looking thoughtful.
‘What? Isn’t there just a password?’
‘Oh no, you’ve got to answer a question,’ said Luna.
‘What if you get it wrong?’
‘Well, you have to wait for somebody who gets it right,’ said Luna. ‘That way you learn, you see?’
‘Yeah . . . Trouble is, we can’t really afford to wait for anyone else, Luna.’
‘No, I see what you mean,’ said Luna seriously. ‘Well then, I think the answer is that a circle has no beginning.’
‘Well reasoned,’ said the voice, and the door swung open.”
— J.K. Rowling (Harry Potter and the Deathly Hallows (Harry Potter, #7))