I don't recall that being in the books, though maybe it was in the movie or radio show or something.

But "How many roads must a man walk down?" is the 'Question' that the pan-dimensional mice who commissioned the Earth decided to run with to save their careers and possibly lives, after the Earth was destroyed 5 minutes before outputting the final result of its multi-million year computation to determine what the actual Question of life, the universe, and everything, was.

In short: come at me, noob ;-)