In answering this question, we need first of all to establish what an epiphany is. An epiphany can be defined as a sudden great moment of realization, such as that which often precedes a religious conversion. Whether an epiphany is religious or not, the person who experiences it undergoes a radical change.
And that's precisely what happens to the unnamed narrator in Joyce's “Araby.” For much of the story, the young lad was excited about going to the bazaar and buying Mangan's sister, the girl upon whom he has an enormous crush, a nice gift. Thoughts of both the bazaar and Mangan's sister fill the boy's every waking hour, giving his otherwise drab, humdrum existence some much-needed color and excitement.
However, when the boy finally reaches the bazaar towards the end of the story, he experiences an epiphany in which he realizes that the color, romance, and excitement he'd previously associated with the bazaar was all just a mirage. He's arrived at the bazaar too late, just as the stalls are closing down. In the darkening hall, there is no trace of the exotic or the romantic—just traders packing away their goods, ready to be sold another day.
As a result of his epiphany, the boy becomes thoroughly disillusioned—not only that, but hurt, angry, and humiliated. All of a sudden, he's been unceremoniously dumped back into the everyday world he'd tried so hard to escape.