“Even so… to trust your future to some frail craft speeding through the unknown void, prey to unthinkable dangers…”
“That was what the dinosaurs did,” said Ridcully. “And the crabs. And all the rest of them.”
“I beg your pardon?”
“I meant that this world is a pretty frail craft, if you take the long view.”

– a frail craft |
Terry Pratchett, Ian Stewart, and Jack Cohen, The Science of Discworld III: Darwin’s Watch