The symbolism is clear here, and it is troubling and terrible to the girl. Finally, the girl and the boy have totally different reactions to the man and his situation. The girl feels sorry for him, and realizes she is witnessing something important, although she cannot find the words to express what that is. She dances with him, and feels an emotional connection with him, while the boy just gets drunk. He writes the check to buy the furniture, and has no other emotions about what is happening, it is not real, or it is not important to him. In that reaction, he could be very much like the drunken man as he grows older, and the girl may be witnessing her own future, which is even more frightening to her. The boy is kind of clueless about the situation, which is why he does not try to communicate about it later. He just accepts it and moves on. However, it changes the girl and her outlook, and that is why she feels the need to talk about it, even if she cannot find the right words to say exactly how she feels.

The young girl cannot find the words to express what she has seen, just as the man cannot seem to find the words, either. The young girl has seen a side of life that is all too real, and it has affected her, because she recognizes, even if she will not admit it, that the same thing could happen to her and the young boy in the future, and that is terribly frightening to think about and remember. She learns about life, and it is a lesson she will certainly not forget. She also learns that there are situations that just do not have the right words to discuss them, and this is troubling to her, too. In effect, she may have seen her own future, and learned far more than she would like to know about life.
References

Carver, Raymond. "Why Don't You Dance?" Nasonart.com. 2008. 21 April 2008. http://www.nasonart.com/personal/lifelessons/WhyDon%27tYouDance.html