J.k. Rowling said this quote

“ Hermione, if Harry’s seen a Grim, that’s — that’s bad,” he said.“My — my uncle Bilius saw one and — and he died twenty-four hours later!”“Coincidence,” said Hermione airily, pouring herself some pumpkin juice.“You don’t know what you’re talking about!” said Ron, starting to get angry. “Grims scare the living daylights out of most wizards!” “There you are, then,” said Hermione in a superior tone. “They see the Grim and die of fright. The Grim’s not an omen, it’s the cause of death! And Harry’s still with us because he’s not stupid enough to see one and think, right, well, I’d better kick the bucket then! ”