4 ideas
Sitting on a bench in the Bouville public park, Antoine Roquentin stares at the black, knotted root of a chestnut tree and suddenly cannot see it as a 'root' at all. The word, its function and its category fall away, and what is left is a shapeless, swollen mass that is simply there, too much and for no reason. The revelation makes him physically sick, and it is the scene in which his 'nausea' finally gets a name: existence itself.
Nothing that exists has a reason or necessity for existing. Things, and people, are simply 'de trop', in excess, and could just as well not be there. Explanations and causes describe how things relate to each other, but they never ground the brute fact that anything exists at all.
A lived life is a shapeless run of moments, one added to the next without meaning. The sense of an 'adventure', with a beginning that points toward an end, is imposed afterward by narration, which reads events backward from their conclusion. To live as if telling your life is therefore a self-deception: you have to choose between living and recounting.
Names, categories and functions work like a surface coating that makes objects look tame, usable and familiar. When that coating slips, as with a seat that stops being a 'seat' or a hand that stops being a 'hand', the thing shows itself as a raw, alien presence that exceeds every word for it. On this view everyday order is a practical fiction laid over a world that has no built-in meaning.