Zaphod thinks they're on a mythic quest to find the lost planet Magrathea. They've found a lost planet alright, orbiting twin stars, but Ford still doesn't believe.

As Ford gazed at the spectacle of light before them excitement burnt inside him, but only the excitement of seeing a strange new planet; it was enough for him to see it as it was. It faintly irritated him that Zaphod had to impose some ludicrous fantasy onto the scene to make it work for him. All this Magrathea nonsense seemed juvenile. Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?