Presumably, everyone knows that "To be, or not to be" is a phrase from Shakespeare's Hamlet.
Same goes for "something is rotten in the state of Denmark." And many people might correctly guess that "Get thee to a nunnery" is from Hamlet as well.
But what about "the lady doth protest too much"?
"To thine own self be true"?
"Neither a borrower nor a lender be"?