Time is a drug. Too much of it kills you.

Every intelligent being, whether it breathes or not, coughs nervously at some time in its life.

In the beginning there was nothing, which exploded.

That's Third Thoughts for you. When a huge rock is going to land on your head, they're the thoughts that think: Is that an igneous rock, such as granite, or is it sandstone?

What's a philosopher?' said Brutha.
Someone who's bright enough to find a job with no heavy lifting,' said a voice in his head.

Don't you understand?" snarled Rincewind. "We are going over the Edge, godsdammit!"
"Can't we do anything about it?"
"No!"
"Then I can't see the sense in panicking," said Twoflower calmly.