Being stupid means avoiding thinking by jumping to conclusions.

<nowiki/>'Most beautiful dumb girls think they are smart and get away with it, because other people, on the whole, aren't much smarter.

"Oh," the figure settled back down, "those reasons. Well, yes. Clever, even. But still profoundly stupid."

I used to think she was quite intelligent , in my stupidity. The reason I did was because she knew quite a lot about the theater and plays and literature and all that stuff. If somebody knows quite a lot about all those things, it takes you quite a while to find out whether they're really stupid or not.

It is man's intelligence that makes him so often behave more stupidly than the beasts. ... Man is impelled to invent theories to account for what happens in the world. Unfortunately, he is not quite intelligent enough, in most cases, to find correct explanations. So that when he acts on his theories, he behaves very often like a lunatic. Thus, no animal is clever enough, when there is a drought, to imagine that the rain is being withheld by evil spirits, or as punishment for its transgressions. Therefore you never see animals going through the absurd and often horrible fooleries of magic and religion. No horse, for example would kill one of its foals to make the wind change direction. Dogs do not ritually urinate in the hope of persuading heaven to do the same and send down rain. Asses do not bray a liturgy to cloudless skies. Nor do cats attempt, by abstinence from cat's meat, to wheedle the feline spirits into benevolence. Only man behaves with such gratuitous folly. It is the price he has to pay for being intelligent but not, as yet, intelligent enough.

Let’s define dumb as being different from stupid. Dumb means you don’t know what you’re supposed to know. Stupid means you know it but make bad choices. […] Dumb used to be a by-product of lack of access, bad teachers, or poor parenting. Today, dumb is a choice, one that’s made by individuals who choose not to learn. If you don’t know what you need to know, that’s fixable. But first you have to want to fix it.

If Diddy already knows what he does that's foolish and stupid, why can't he become wise? Act wisely. For, oh, Diddy has perceived his follies countless times. Is heartily ashamed of them, strenuously repudiates them. It's only that he doesn't understand. Not really. A hopeless, bumbling tourist in the somber labyrinth of his own consciousness.

Ordinarily he is insane, but he has lucid moments when he is only stupid.

One of the major difficulties Trillian experienced in her relationship with Zaphod was learning to distinguish between him pretending to be stupid just to get people off their guard, pretending to be stupid because he couldn't be bothered to think and wanted someone else to do it for him, pretending to be outrageously stupid to hide the fact that he actually didn’t understand what was going on, and really being genuinely stupid. He was renowned for being amazingly clever and quite clearly was so — but not all the time, which obviously worried him, hence, the act. He preferred people to be puzzled rather than contemptuous.

An educated woman is a stupid woman

The more stupid one is, the closer one is to reality. The more stupid one is, the clearer one is. Stupidity is brief and artless, while intelligence squirms and hides itself. Intelligence is unprincipled, but stupidity is honest and straightforward.

No intelligent idea can gain general acceptance unless some stupidity is mixed in with it. Collective thought is stupid because it's collective. Nothing passes into the realm of the collective without leaving at the border — like a toll — most of the intelligence it contained.

In youth we're twofold. Our innate intelligence, which may be considerable, coexists with the stupidity of our inexperience, which forms a second, lesser intelligence. Only later on do the two unite. That's why youth always blunders - not because of its inexperience, but because of its non-unity.

Today the only course left for the man of superior intelligence is abdication.

He may look like an idiot and talk like an idiot but don't let that fool you. He really is an idiot.

When someone says "I am not that stupid," it often means that he is more stupid than he thinks.