To clarify for the people who are mildly interested about such things, I am reading a version of the book with this blue cover on the left. Which looks good and interesting, but not as much as this awesome-looking red cover on the right. In my opinion, the cover art is as much a part of the reading experience as the prose itself, and I just don't understand the people who don't like the new red covers (other Penguin classics have also been re-covered) - as someone who fits the "young consumer" demographic, I do find that they look very intriguing and "maybe I could buy it?"-worthy.
Enough rant, on to existentialism!
First, the narrator interrupts himself (rudely) in his own writing. Then, he goes no the talk about how reason is good for the intellect, while volition ("making up your mind") will include both a person's reason and their speculations.
Then, the word "rubbishy" is used!
A person's capacity for living goes beyond their reason, which is only their conscious mind; a person's will also includes their unconscious mind. The narrator then defines "man" as "a creature that has two legs and no sense of gratitude".
Finally, since people HATE the idea of being predictable according to known "laws of nature", they will also willfully do irrational, harmful things, just to convince themselves that they cannot be predicted.
Narrator: "I'm joking, and terrible at it!" Can't say I disagree.
Man loves to build, and roads are a particular favorite, and mankind's propensity to destruction and chaos stems from the fear of ever attaining the end of their road, of finishing what they've begun. The process is, to man, more important that the final product; this is parallel to our attitude about life and death.
What is good for man? Not just what is normal and positive; suffering is as important as prosperity. Smashing things can be pleasant. "Consciousness is infinitely greater than [...] two and two make four."
Some talk about the "Palace of Crystal", an idealization that is eternally perfect and inviolable. The narrator rejects it for these very reasons. He then states that to live is to want - for food when you're hungry, for example.
After skipping over a bit about desire, we get to the point where the narrator expresses his certainty that "underground people" like him, able to keep silent for 40 years, should be kept in check lest they be loosed upon the world, whence they will talk and talk and talk. What does he mean by "underground people"? People who bury themselves under their facade of respectability and clam, people who, instead of expressing themselves, opt for a more "normal" act?
Conscious inertia is the best! And even though he is envious of them, the narrator would never want to be a normal man. He then states that he doesn't believe a word that he's written down so far (I've just read 42 pages of lies?!), and he wants to say something, but lacks the resolution to express it. The narrator then asks himself why he writes as though he had an audience, since he has no desire to get his manuscript published.
He muses on the fact that everyone lies to themselves, and that the more respectable a man is, the more things about himself he is afraid of becoming aware of - for that reason, truthful autobiographies are an impossibility.
To conclude this part, the narrator says he writes because there's something about written words that make the concepts they express more awe-inspiring than remembered words alone. Also, writing could be good therapy for him. Plus, he's dreadfully bored and it's something to do.