10 Harry Potter Mysteries JK Rowling Has Actually Answered

In The Order Of The Phoenix, Harry suddenly sees that the carriages up to Hogwarts that are used by all but First Years are not pulled by magic, but by Thestrals. For the first time, he can see them. It is explained to him that this is because he has experienced death, and it becomes clear that the death in question was the murder of Cedric Diggory at the hands of Lord Voldemort the previous summer.

Why, though, couldn't this boy see them from the beginning? An orphan whose parents were killed before his very eyes?

To best answer this one fully, here is JK Rowling's answer:

I’ve been asked this a lot. Harry didn’t see his parents die. He was in his cot at the time (he was just over a year old) and, as I say in ‘Philosopher’s Stone’, all he saw was a flash of green light. He didn’t see Quirrell’s death, either. Harry had passed out before Quirrell died and was only told about it by Dumbledore in the last chapter.

He did, however, witness the murder of Cedric, and it is this that makes him able to see the Thestrals at last. Why couldn’t he see the Thestrals on his trip back to the train station? Well, I didn’t want to start a new mystery, which would not be resolved for a long time, at the very end of the fourth book.

I decided, therefore, that until Harry is over the first shock, and really feels what death means (ie, when he fully appreciates that Cedric is gone forever and that he can never come back, which takes time, whatever age you are) he would not be able to see the Thestrals. After two months away from school during which he has dwelled endlessly on his memories of the murder and had nightmares about it, the Thestrals have taken shape and form and he can see them quite clearly.