6 ideas
Palomar stands on the shore and tries to watch one wave from its beginning to its end, but each wave overlaps with the ones before and after it and gets folded back by the undertow, so he can't find where it starts or stops. Every time he thinks he has pinned the pattern down, a new variation spoils it. He leaves irritated, having learned that isolating one object means cutting it out of a system in which it is never actually separate.
Palomar keeps finding that his effort to see things neutrally is shaped by where he stands, what he is feeling, and what he wants from the looking. The sun's reflection on the sea runs straight toward whoever is watching it.
Palomar weeds his lawn and has to decide which plants belong and which count as weeds. As he tries to count and name each blade, 'the lawn' breaks apart into a crowd of competing species, and it turns out to be a human category imposed on a mixed and shifting population. Trying to govern the whole makes it clear that the whole was never a natural unit to begin with.
Palomar's rule of describing only what can be seen, and seeing it completely, leads each time to more detail than he can take in and to distinctions that keep branching. Pushing hard for exactness does not produce certainty. It shows how much any description has to leave out.
The pieces are grouped by a threefold scheme, repeated at each scale. First comes visual description of the thing itself, then the cultural and anthropological meanings it carries, and finally speculation about the cosmos, time, and the self.
Near the end Palomar decides to act as though he were dead, hoping that removing himself will let him see the world as it is without him. The effort fails, because even imagining his absence requires a self to do the imagining, and the world he pictures still sets out things for him to notice. Getting the observer out of the picture turns out to be impossible, since the effort to erase the self is just another act that self performs.