It’s all Greek to me: I don’t understand it at all

Example: I don’t understand this contract. It’s all Greek to me.”
Origin: At least two different playwrights used this phrase during one of their plays in the 17th century, those being Thomas Dekkar and William Shakespeare. In 1603, Dekkar’s play Patient Grissel reads:
“FAR: Asking for some Greek poet, to him he fails. I’ll be sworn he knows not so much as one character of the tongue.
RIC: Why, then it’s Greek to him.”
The saying was also used in 1616 in Shakespeare’s play Julius Caesar:
“CASSIUS: Did Cicero say any thing?
CASCA: Ay, he spoke Greek.
CASSIUS: To what effect?
CASCA: Nay, an I tell you that, I’ll ne’er look you i’ the face again: but those that understood him smiled at one another and shook their heads; but, for mine own part, it was Greek to me.”