How we cite our quotes: (Chapter.Paragraph)
Quote #1
This planet has—or rather had—a problem, which was this: most of the people on it were unhappy for pretty much of the time. Many solutions were suggested for this problem, but most of these were largely concerned with the movements of small green pieces of paper, which is odd because on the whole it wasn't the small green pieces of paper that were unhappy. (Introduction.3)
Foolishness is clearly related to sadness here: we're not happy, but we're too foolish to find a way out of that unhappiness. Notice also that Adams gets in a little dig about something that a lot of people think will make them happy—money, those "small green pieces of paper." We only think money will make us happy because we're not smart. Does this make anyone else want to take a day off and go to the beach?
Quote #2
Pages one and two had been salvaged by a Damogran Frond Crested Eagle and had already become incorporated into an extraordinary new form of nest which the eagle had invented. It was constructed largely of papier-mâché and it was virtually impossible for a newly hatched baby eagle to break out of it. The Damogran Frond Crested Eagle had heard of the notion of survival of the species but wanted no truck with it. (4.42)
Foolishness isn't just for humanoids anymore. Here the Damogran Frond Crested Eagle has used parts of Zaphod's speech to make a nest that won't work. But note that this type of foolishness is associated with some type of smarts: the eagle has invented this new nest type, which must take some intelligence to do.
Quote #3
Meanwhile, the natural forces on the planet Vogsphere had been working overtime to make up for their earlier blunder. They brought forth scintillating jeweled scuttling crabs, which the Vogons ate, smashing their shells with iron mallets; tall aspiring trees with breathtaking slenderness and color which the Vogons cut down and burned the crab meat with; elegant gazelle-like creatures with silken coats and dewy eyes which the Vogons would catch and sit on. They were no use as transport because their backs would snap instantly, but the Vogons sat on them anyway. (5.4)
And foolishness isn't just for individuals anymore—now you can buy it in bulk for a whole species. The Vogons are foolish bureaucrats (see our breakdown of Politics in "Themes"), but they're also foolish and cruel. That is, here they are, totally abusing the natural resources of their planet, because this is either all they can think to do or because they're jerks. Notice how Adams uses adjectives to make sure we know who is beautiful here: "scintillating jeweled" crabs are pretty; "iron mallets" aren't so pretty. Heck, the Vogons can't even cook their crab properly but end up with "burned" crab meat.