"Describe worrying," he went on.
"What!?"
"Pretend I'm someone who has never worried. I'm mystified. It don't get it. Tell me how to worry."
"Well... I guess the first step is to envision a sequence of events as they might play out in the future."
"But I do that all the time. And yet I don't worry."
"It is a sequence of events with a bad end."
"So, you're worried that a pink dragon will fly over the concent and fart nerve gas on us?"

Orolo and Erasmas, Part 4, "Anathem" - Anathem (2008)