Perspective
For Arthur, his house is a central part of the life he knows, which is why he is so upset when it is set to be demolished. However, it is clear that the man seeking to demolish the house sees the house only as a nuisance in the way of the bypass.
A similar scenario occurs in the story on a much larger scale. To Arthur and his fellow human beings, the Earth is all they know. However, it is destroyed by a fleet of Vogon ships to create an interstellar expressway. They think nothing of destroying the Earth with all of its life and history because to them it is just a roadblock. Adams encourages readers to think beyond their limited perspective and consider the vastness, weirdness, and incomprehensibility of the rest of the universe.
Cluelessness
Arthur Dent is clueless in every way, but he represents the entire population of the Earth before it was destroyed. Humans seem to think they are the dominant species on the planet, completely oblivious to the fact that the planet is being run by mice, as well as the virtual center of the universe.
Cluelessness is also obvious in other main characters. Zaphod is the president of the Universe, but he struggles to figure out why he ever sought that position and what he is doing with the Heart of Gold. Trillian and Arthur are clueless simply because the Earth was all they ever knew, and now it is apparently gone. Ford is clueless regarding others in general, as he is only focused on himself and doesn't often pick up on up social cues. Adams suggests that life can be strange and confusing: when we only come at it with our limited perspective, and ignorance we end up not fully engaging and stumbling awkwardly about, looking for meaning. This is why the Guide is so important: it helps us figure out our world and the worlds beyond.
Chance and Coincidence
Adams makes it clear there is no God, no pantheon, no meta-narrative, no karma, no fate, etc. His universe is ordered only along the lines of cause and effect, chance and coincidence, past, present, and future. Improbable things happen and there is little one can do to prepare for them. It is a universe in which one's actions are all one has and essentially all that matters. Adams suggests there's little point to having expectations or considering yourself part of a larger plan: you are merely here and now, and you ought to make the most of it.
Discovery
The discovery that there is more to the Universe than just the Earth is a big one for Arthur Dent. When his home and planet are destroyed, he is sent on wild journey through space, seeing lost planets, large black clouds, aliens, and several star systems in the Galaxy. Although it is all a completely new and quite terrifying experience for Arthur, he learns new lessons on the way and eventually makes friends with his fellow hitchhikers. Discovery is thus a vital part of existence and one should not mourn too much the loss of comfort and routine: there is much to learn and much to experience.
Power
In this Universe, power is often—or, at the very least, in the hands of seemingly very unlikely creatures. Zaphod is President of the Galaxy, but other, unknown entities are really calling the shots. Humans are not at all as powerful as they think they are: both mice and dolphins are smarter than they are, and a disgusting, evolutionarily primitive race destroyed their whole planet. A robot with a massive brain isn't powerful at all, and the (2nd) smartest computer ever needs millions of years to figure out a Question. Thus, power is conceived in different ways than readers might expect.
Communication
In many respects, communication is not easy for the characters in the novel. There are many different languages, and people don't say what they mean or know why they say something. They don't have the ability to articulate their thoughts, and verbal irony is ubiquitous. Ford, for example, communicates in a way that is very difficult for Arthur and for all humans. He says things in a way that suggests they aren't that important—and to him they are not—but that to us seem to necessitate a much different tone or word choice. He tells the barman he wants six pints of bitter, "And quickly please, the world's about to end" (21). He often tells Arthur not to panic when Arthur, by most standards, should panic since everything he knew just blew up. Good communication is crucial, however, in surviving the dangers of the Galaxy. The Babelfish, named after the biblical Tower of Babel, is an ingenious way for people to communicate (it's no wonder that one of the first language translators on the internet was called Babelfish).
The Value of Knowledge
Adams's Universe might be a crazy, wild, dangerous, and unpredictable place, but at least there's a way to learn how to navigate it: the Hitchhiker's Guide to the Galaxy. Some knowledge, however limited, is better than none. The Guide allows travelers to delve into the history and background of any matter of subject so they can be prepared for whatever circumstances they find themselves in. For Arthur, who knows nothing of the Universe beyond now-destroyed Earth, the Guide is invaluable. Adams is enthusiastic about the value of having such knowledge at one's fingertips, as well as knowledge that is easily understood and intellectually accessible. Curiosity is thus very much a cherished and useful virtue.
