In hindsight, I cannot believe I didn't know the fate of Cedric Diggory when I first read the Harry Potter books. I was an incredibly late bloomer with the series (I read all of them after my Sophomore year of college), and when I started The Sorcerer's Stone, the only characters whose doomed fate I knew about were Dumbledore and Fred Weasley. Nobody else; not Sirius Black, Snape, Lupin, Dobby, Hedwig. I didn't even know that Sirius would ultimately turn out to be a good guy; that's how Harry Potter ignorant I was going into this.
I'm so glad that most of these moments were not spoiled for me. Cedric's demise was a genuine surprise and really served as a turning point for the whole series. Things got real after Goblet of Fire, and even though the death of a young character was sad, that doesn't mean we can't laugh about "That's my boy!!!" memes now.