Status Updates From Small Gods (Discworld, #13)

How did he know the sky was blue? It was just something in his head. You couldn’t think about how you thought. It was like opening a box with the crowbar that was inside. […]
Brutha tried to put it out of his mind, which was like trying to empty a bucket underwater.

Fear is strange soil. Mainly it grows obedience like corn, which grows in rows and makes weeding easy. But sometimes it grows the potatoes of defiance, which flourish underground.