But we've seen that character flaw of having to be right (even when she's wrong) all through the books. Just look at the first book, when she could have led to Harry's death by setting Snape on fire while he was saving Harry's arse. Rather than admit that maybe she got it wrong, she was still going around insisting to Hagrid and the boys that she *knew* Snape was hexing Harry, because she "knew" what spells looked like. She flat out refused even to acknowledge that perhaps counter-spells might look that way as well.