Disdaining 19th-century notions that character development in novels should obey and reveal psychological law, La Nausée treats such notions as bourgeois bad faith, ignoring the contingency and inexplicability of life.
From the psychological point of view, Antoine Roquentin could be seen as an individual suffering from depression, and the Nausea itself as one of the symptoms of his condition. Unemployed, living in deprived conditions, lacking human contact, being trapped in fantasies about the 18th century secret agent he is writing a book about, he establishes Sartre's oeuvre as a follow-up to Dostoevsky's Crime and Punishment, or Rilke's The Notebooks of Malte Laurids Brigge in search of a precise description of schizophrenia. Rilke's character anticipates Sartre's.
However, Roquentin's predicament is not simply depression or mental illness, although his experience has pushed him to that point. Sartre presents Roquentin's difficulties as arising from man's inherent existential condition. His seemingly special situation (returning from travel, reclusiveness), which goes beyond the mere indication of his very real depression, is supposed to induce in him (and in the reader) a state that makes one more receptive to noticing an existential situation that everyone experiences, but may not be sensitive enough to let become consciously noticeable. Roquentin undergoes a strange metaphysical experience that estranges him from the world. His problems are not merely a result of personal insanity, which would be deprived of larger significance. Rather, like the characters in the Dostoevsky and Rilke novels, he is a victim of larger ideological, social, and existential forces that have brought him to the brink of insanity. Sartre's point in Nausea is to comment on our universal reaction to these common external predicaments.
Hayden Carruth wrote of the way that "Roquentin has become a familiar of our world, one of those men who, like Hamlet or Julien Sorel, live outside the pages of the books in which they assumed their characters ... It is scarcely possible to read seriously in contemporary literature, philosophy, or psychology without encountering references to Roquentin's confrontation with the chestnut tree, for example, which is one of the sharpest pictures ever drawn of self-doubt and metaphysical anguish. ... Certainly, Nausea gives us a few of the clearest and hence most useful images of man in our time that we possess; and this, as Allen Tate has said, is the supreme function of art."
More recently, younger French academics following Emmanuel Legeard have rather built upon cultural psychology to interpret the nausea feeling more metaphorically: «The feeling of nausea has spawned a series of implausible interpretations, but any truly involved reader should be able to apprehend through intuitive sympathy that nausea is disgust at the traumatic decomposition of the divine within existence, symptomatic of the discovery of the absurd, of the disenchantment of the world. Transcendence and providence were invented by man. Every being is meaningless "in itself". There is no God. But the experience through nausea ends up taking a positive turn: if God doesn't exist, then everything becomes possible. And that's how, with despair, true optimism begins.»