Harry Potter and the Deathly Hallows
How we cite our quotes:
Harry thought fast, his scar still prickling, his head threatening to split again. Dumbledore had warned him against telling anyone but Ron and Hermione about the Horcruxes. Secrets and lies, that's how we grew up, and Albus… he was a natural… Was he turning into Dumbledore, keeping his secrets clutched to his chest, afraid to trust? But Dumbledore had trusted Snape, and where had that led? To murder at the top of the highest tower… (29.44)
Harry's torn between his natural impulse to trust his friends in the DA, who have proven themselves worthy of his belief, and his fear of betrayal. However, thinking through Dumbledore's error of too much secrecy, he goes with his instincts and trusts his friends, just as he did in the beginning of the book.
"So the boy… the boy must die?" asked Snape quite calmly.
"And Voldemort himself must do it, Severus. That is essential."
Another long silence. Then Snape said, "I thought… all these years… that we were protecting him for her. For Lily."
"We have protected him because it has been essential to teach him, to raise him, to let him try his strength," said Dumbledore, his eyes still tight shut. "Meanwhile, the connection between them grows ever stronger, a parasitic growth: Sometimes I have thought he suspects it himself. If I know him, he will have arranged matters so that when he sets out to meet his death, it will truly mean the end of Voldemort."
Dumbledore opened his eyes. Snape looked horrified.
"You have kept him alive so that he can die at the right moment?... You have used me… I have spied for you and lied for you, put myself in mortal danger for you. Everything was supposed to keep Lily Potter's son safe. Now you tell me you have been raising him like a pig for slaughter…" (33.182-185)
This is a kind of double betrayal on Dumbledore's part – of Snape, and of Harry himself. We feel cheated, just as Snape does – how could Dumbledore manipulate them (and us) like that?
Dumbledore's betrayal was almost nothing. Of course there had been a bigger plan; Harry had simply been too foolish to see it, he realized that now. He had never questioned his own assumption that Dumbledore wanted him alive. Now he saw that his life span had always been determined by how long it took to eliminate all the Horcruxes. (34.6)
The betrayal here stems again from the idea of "For the Greater Good" – Dumbledore seems to have chosen Harry to die, since he had already been chosen to die once, in order to save the rest of the world… he just never informed Harry of this decision. Whoops.