Vincent Crabbe hated mudbloods. His parents said that they were dirty, filthy animals who didn't deserve a place in the world. He believed them. He grew up believing them. But as the war wore on, it got harder to hold onto that. First they were making the world better, the Dark Lord was purging the unclean and cancerous rot of mudbloods from their society. But then they started killing halfbloods. And then purebloods. And then anyone who wouldn't take the mark, who wouldn't kneel. Draco was sick, worn thin as a ghost in the honor of the Dark Lord's service. The Malfoys in general were treated like slaves, and Vincent was starting to realize that the Dark Lord didn't really believe the things he said. Maybe they weren't really true?
And then the war ended. Harry Potter, specky, scrawny Harry Potter, faced down the Dark Lord and won. He heard rumors that he'd done the impossible, that he'd sacrificed himself, died and come back. Harry Potter, the halfblood. And then the world changed again. Tom Marvolo Riddle, the Dark Lord Voldemort, the halfblood. Vincent's parents had been wrong, he'd been wrong. His blood hadn't made him special, it hadn't made him powerful, it hadn't made him right.
Vincent Crabbe was never a very smart man. The few things he thought he knew turned out to be wrong, and he didn't know where to go. There was nowhere to go. A year, one year in Azkaban. Goyle got three. He wasn't sure why the court was so lenient with him, he certainly hadn't had enough gold to pay them to be, but they were. He heard someone say that they'd pitied him, too stupid to see through the lies his parents fed him. He hadn't processed the words fast enough to react, he'd always been a bit slow, and when he turned to shout in the face of the person who said it they were already gone.
One year. One year of Azkaban, one year of solitude, one year locked up with noone but himself for company. Vincent Crabbe was never a smart man, but he hated being wrong. He was sick of it. Sick of being stupid, sick of being foolish, sick of being wrong. They'd let him out in year, and he'd have nothing and nowhere to go, but Vincent knew one thing. He wouldn't leave this cell still being wrong. He'd figure out how to be right, he'd do it even if it killed him.