The story opens on the day before Christmas. Della has been struggling to save enough money to buy a Christmas present for her beloved husband Jim - an enormously difficult process because of the small amount she receives for household expenses. She has just finished counting the amount she has been able to save, and is realizing that it is not enough to purchase the type of present she wants to give Jim.
One dollar and eighty-seven cents. That was all...There was clearly nothing to do but flop down on the shabby little couch and howl. So Della did it.
Della is unhappy because she doesn't know what to do, how to go about raising more money so she can buy a present "just a little bit near to being worthy of the honor of being owned by Jim."
One dollar and eighty-seven cents.
This opening sentence immediately identifies the problem and the protagonist. Della Young would like to buy her husband a really good Christmas present, but she doesn't have enough money. Her motivation creates her problem. The motivation leads her to attempt to solve her problem by selling her beautiful long hair. But this creates another problem. Now she is afraid that Jim won't love her without her beautiful long hair. The coins amounting to $1.87 symbolize both her motivation and her problem. Obviously she can't buy much of a present with such a small sum of money, and she would probably feel ashamed to give her husband a gift that would cost so little. In those days she might have been able to buy a necktie or a box of three handkerchiefs with that amount of money.
Della is unhappy because she doesn't have enough money to buy her husband a good present, and she continues to be unhappy because she is ashamed of the way she looks in the mirror after she has had all her hair cut off. She becomes happy at the end because her husband assures her that he loves her and will always love her. The fact that he has sold his treasured watch in order to buy a special present for her is tangible proof of his love. In fact, they have both proved by their sacrifices how much they truly love each other.
This is probably O. Henry's most popular story because it involves a problem which most of us can relate to. Most of us wouild like to buy something that we can't afford. The fact that we can't afford it doesn't keep us from wanting it.