A short story about maturation and coming of age, Katherine Mansfield's "Her First Ball" uses as one of its primary themes the conceptualization of life as it is, and not as our circumstances, or our surroundings, try to show it to us.
Notice how Leila, an impressionable, young middle class girl, approaches her first ball with the degree naivite and innocence that instills in the reader the need to view her first ball as a grandiose event. Each description of what Leila sees is carefully crafted by Mansfield to place emphasis on things that are actually, quite fake: aesthetics, glitter, glitz, dresses that are only worn once or twice, beautiful people, the glorious music, and the joy of the moment.
The addition of the fat man is basically an allegory to the break with the fantasy of the hour, and the sudden entrance of reality in a supreme moment of blitz. It happens to all of us in real life, however, in Mansfield's story, it is represented by the entrance of this ugly person in Leila's perfect little moment.
As she feels obligated to conform to the man's wish to dance with her, we see how her dance is actually a symbol of that moment when we open our eyes and see what life is really all about. In Leila's character, this moment happens when the fat man talks to her about aging, death, the loss of beauty, and other realities that do not go in tandem with the moment in time in which they are coexisting.
And you'll smile away like the poor old dears up there, and point to your daughter, and tell the elderly lady next to you how some dreadful man tried to kiss her at the club ball. And your heart will ache, ache [...]-"because no one wants to kiss you now. And you'll say how unpleasant these polished floors are to walk on, how dangerous they are. Eh, Mademoiselle Twinkletoes?" said the fat man softly.
At this point, Leila is sickened to listen to this and she basically wants to stop the dance. This is also allegorical: should we stop living, at all, just because one beautiful moment does not, or will not, last forever? Is it worth not continue to dance (living) just because life will not always be "a ball?". This is a moment of maturation for Leila, and this is why her reaction is to be shocked at the possibility. This is, after all, her first ball. She may think life will always be like this, and that she will always be young and beautiful. To any young woman like her, this is a first realization.
I want to stop," she said in a breathless voice. The fat man led her to the door.
"No," she said, "I won't go outside. I won't sit down. I'll just stand here, thank you." She leaned against the wall, tapping with her foot, pulling up her gloves and trying to smile. But deep inside her a little girl threw her pinafore over her head and sobbed. Why had he spoiled it all?
However, we know that in the end Leila finds another dancing partner and somehow her demeanor changes to one which is more serious, haughty and less shy than before. This is because although the words she heard were harsh, she is now one-step more mature just for having learned them.
The lights, the azaleas, the dresses, the pink faces, the velvet chairs, all became one beautiful flying wheel. And when her next partner bumped her into the fat man and he said, "Pardon," she smiled at him more radiantly than ever. She didn't even recognise him again.