Quote 1
"There have been too many mistakes where Harry Potter is concerned. Some of them have been my own. That Potter lives is due more to my errors than to his triumphs." (1.32)
Voldemort here is certain that everything that happens is up to him – and nobody else. The only choices that matter in his mind are his own, a belief that really betrays his arrogance.
Quote 2
"One of us?" jeered Voldemort, and his whole body was taut and his red eyes stared, a snake that was about to strike. You think it will be you, do you, the boy who has survived by accident, and because Dumbledore was pulling the strings?"
"Accident, was it, when my mother died to save me?" asked Harry. […] "Accident, when I decided to fight in that graveyard? Accident, that I didn't defend myself tonight, and still survived, and returned to fight again?"
"Accidents!" screamed Voldemort, but still he did not strike. […] "Accident and chance and the fact that you crouched and sniveled behind the skirts of greater men and women, and permitted me to kill them for you!" (36.95-97)
Yet again, Voldemort makes the fatal error of underestimating the choices and deliberate actions of others, assuming that only his choices matter.
Quote 3
"I regret it," said Voldemort coldly.
He turned away; there was no sadness in him, no remorse. It was time to leave this shack and take charge, with a wand that would now do his full bidding… Voldemort swept from the room without a backward glance… (32.121)
Voldemort's true depths of evil are really revealed by his callous murder of Snape, who he thought was his faithful servant all these years. He truly has progressed beyond "the usual evil" – he's past all human feeling.
Quote 4
"You show spirit and bravery, and you come of noble stock. You will make a very valuable Death Eater. We need your kind, Neville Longbottom."
"I'll join you when hell freezes over," said Neville. "Dumbledore's Army!" he shouted, and there was an answering cheer from the crowd… (36.54)
Neville's good-evil compass never wavers, even when Voldemort tries to tempt him over to the dark side. It would never work – he's a true Gryffindor through and through, and is loyal and courageous to the bone. He's certainly not the second coming of Peter Pettigrew, as we once feared.
Quote 5
"Is it love again?" said Voldemort, his snake's face jeering. "Dumbledore's favorite solution, love, which he claimed conquered death, though love did not stop him falling from the tower and breaking like an old waxwork? Love, which did not prevent me from stamping out your Mudblood mother like a cockroach, Potter – and nobody seems to love you enough to run forward this time and take my curse. So what will stop you from dying now when I strike?" (36.102)
After all these years, Voldemort still hasn't learned his lesson – love does matter, and it is a kind of power he'll never be able to master. Love as a motivation is what has undone him; we've seen it in everyone who's betrayed the Dark Lord, like Snape and Narcissa; people can't help but love, and it's the most powerful force in the world.
Quote 6
"Where no proven Wizarding ancestry exists, therefore, the so-called Muggle-born is likely to have obtained magical power by theft or force.
"The Ministry is determined to root out such usurpers of magical power…" (11.38)
Voldemort's desire to get rid of all non-pureblood Wizards is really a problem of identity – he's taken it upon himself to decide who is really a wizard and who isn't. However, there's the problem of personal identity – Muggle-born wizards really are just as magical as purebloods, and Voldemort's new restrictions are simply lies.