Writing an essay you have no clue about: no knowledge of the the theme; you have enough knowledge of the chosen topic to be dangerous.
Your teacher or professor assigns an essay but doesn't give any further details than word length and due date.
A teacher who receives an essay without having assigned one.
teacher 1: Hey, Chase just gave me an essay and I didn't even assign one!
teacher 2: huh. Have fun grading that guessay!
student 1: Well, seeing that I didn't read the book A Thousand Splendid Suns, I'll get started on that guessay.
student 2: You know she's gonna flunk that guessay!