Once upon a time, when Bellatrix was going to meet Cissy for one of her little sister's Hogsmeade weekends, Bellatrix simply couldn't restrain herself from ripping a book out of a young, greasy-haired student's hand. She was bored with waiting, and her was small and alone – it was a perfect fit for some perfectly legal and innocent torture.
She had caught sight of a passage as she held the open book just out of the skinny boy's reach. She had rather liked it actually:
"Moral indignation is jealousy with a halo."
She couldn't help but remember that quote seven years later, with the same greasy haired boy now a gangling greasy haired young man in front of her, as he enjoyed the sights of his first revel as a bonafide Death Eater.
Back in Hogsmeade that day, he had called her a bully, and every name his eleven year old self could think of as she held his book aloft and he fought back tears.
Now he stood tall before their enemies, fighting back a smirk as he kicked a wand just out of reach of the man who lay before him.
Bellatrix couldn't help but be glad she had pulled that book away from him that day, glad she had done her part to make him the man he was – thirsty for blood and power, and that she had read that bit of book.
After all, it was quite a good quote.