What book is the quote you plunge toward future without a clue form?

The quote "You plunge toward the future without a clue" is from the book "The Hitchhiker's Guide to the Galaxy" by Douglas Adams. It's spoken by the character Ford Prefect, describing the precarious nature of human existence.

The full quote is:

"There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened."

This quote, followed by the line "You plunge toward the future without a clue," highlights the absurdity and uncertainty of life in the face of the vastness of the universe.