The theme of Guy de Maupassant’s “An Adventure in Paris” is the clash between the fantasies that we make up in our minds and reality. This is evident in the fact that the protagonist of the story, a typical, bourgeoise wife, is tired of her traditional life as a wife and mother. In her mind, she dreams of living like those Parisian bohemians she reads about. She feeds herself these ideas from the publications that she reads,

. . . which gave her a glimpse of culpable and ravishing delights, and from her country home, she saw Paris in an apotheosis of magnificent and corrupt luxury.

Therefore, the evidence from the text that shows the clash between fantasy and reality begins with this poignant excerpt. She is basically a traditional, everyday woman desperate to indulge in what she considers to be a much more sophisticated, smart, and glamorous lifestyle in Paris.

However, things do not turn out the way that she expects. She really believed that, upon setting foot in Paris, she would have instantly experienced everything she reads about in the papers: the artists, the bohemians, the debauchery, and the decadence. It is not quite so. Reality was different:

Her relations, who were quite middle-class people, could not introduce her to any of those well-known men with whose names her head was full, and in despair she was thinking of returning

She finally gets a chance to come close to her fantasy when she casually meets the famous author Monsieur Varin. Still determined to live out her fantasies, she forces herself in all the activities of his day, asking him to tell her all about the things she reads about in her magazines. Even then, and as she makes the decision of sleeping with the man as part of her “adventure in Paris,” reality continues to peek in. No matter how hard she tries to fit in, their lives are extremely different, as so are their personalities.

But she was as simple as it was possible for a provincial lawyer’s wife to be, and he was more exacting than a pascha with three tails, and so they did not at all understand each other.

It is then, at the end, when her illusions become entirely deflated. She has the affair, has her day in Paris, but nothing has satisfied her. This famous author that she sleeps with is no longer alluring

she looked, nearly heart-broken, at the little fat man lying on his back, whose round stomach raised up the bed-clothes like a balloon filled with gas.

It is by the end of her “adventure” that there is no doubt that the fantasy of Paris lived only in her mind. Reality is what it is, whether in Paris or in the country. Two clichés that summarize the story’s theme are: “The grass is not always greener on the other side” and “Careful what you ask for, for you may get it.”

It is evident in her final words in the story:

I wanted to know . . . what . . . what vice . . . really was, . . . and . . . well . . . well, it is not at all funny.”

A quote from the story that expresses the theme comes, appropriately, near the very end. The heroine tells the famous man with whom she spent the night:

"I wanted to know . . . what . . . what vice . . . really was . . . and . . . well . . . well, it is not at all funny."

She had long dreamt about the exciting, liberated life she imagined being led by the sophisticated men and women in Paris. Like Mathilde Loisel in Maupassant's "The Necklace," the anonymous heroine of "An Adventure in Paris" is dissatisfied with her humdrum existence as a housewife. She finally goes to Paris with the intention of finding a romantic adventure. She accidentally encounters a famous author whose works have thrilled her. He turns out to be 

...a little, bald-headed, gray-bearded man.

He is also ugly, but the heroine doesn't see the reality because he is none other than the famous Monsieur Varin. She manages to force an acquaintanceship upon him. She seems to be emboldened by the fact that she is finally actually living her dream in Paris where any kind of an adventure can happen, any dream can come true. They spend the day together and then go to bed in his rooms. The affair was a disappointment. He went to sleep and 

...she looked, nearly heartbroken, at the little fat man lying on his back, whose round stomach raised up the bed-clothes like a balloon filled with gas. He snored with the noise of a wheezy organ pipe, with prolonged snorts and comic chokings....and a small stream of saliva was running out of one corner of his half-open mouth.

She is glad when daylight finally appears through the drawn blinds. She is thoroughly disillusioned about the city and about the life she imagined there. The main memory she takes home with her is of the men sweeping what must have been mainly horse manure off the streets.

Maupassant was a realist and a cynic. He was quite familiar with the supposedly fascinating and exciting luxuries and vices of Parisians. He is writing from experience when he describes the rather sordid realities of nineteenth-century Paris. The artists, painters, and musicians gave the place an aura of glamor which did not exist in reality. Maupassant died of syphilis at the age of forty-two.

And it seemed to her as if something had been swept out of her; as if her over-excited dreams had been pushed into the gutter, or into the drain...

An ancient Roman saying pertinent to Maupassant's story is:

Quae e longinquo magis placent

This translates as "Things from afar please the more." Or "Distance lends enchantment."

The girl in Ernest Hemingway's story "Hills Like White Elephants" is expressing the same disillusionment when she says "Everything tastes like licorice." It is sad but true that reality never measures up to our expectations or our dreams.