JK Rowling. Harry Potter and the Deathly Hallows (№ 402183)

Only the difference between truth and lie, bravery and cowardice, ' said Professor McGonagall, turning pale. - In General, just that the difference, which you and your sister do not understand. But there is one thing you will have to understand. You will not be able to blame their eternal stupidity on the Hogwarts students. I will not allow it!