Della is sad because she realizes that she has only a dollar and eighty-seven cents to spend for her husband’s Christmas present.
When Della realizes that is all she has, and he next day is Christmas, she falls on the couch and cries, and then considers that “life is made up of sobs, sniffles, and smiles, with sniffles predominating” (p. 3). She feels sorry for herself because she does not have any money. She also wants to do something nice for her husband.
Della has earned her pennies “two at a time” by bargaining prices down when shopping, which is very embarrassing. She feels bad because she worked so hard, and has so little to show for it. It is this preoccupation with money and gifts that causes Della to do the unthinkable and sell her hair for more money. As we learn later, her husband does the same thing.
And here I have lamely related to you the uneventful chronicle of two foolish children in a flat who most unwisely sacrificed for each other the greatest treasures of their house. (p. 6)
In the end, they learn that money does not bring happiness-love does. They learn to be wise, and appreciate not what they don't have but what they do have- one another.