The irony in "The Gift of the Magi" is that the two main characters get each other Christmas gifts they cannot use. The gifts are unusable because of sacrifices they made to buy them.
In this classic tale by author O. Henry, Della and Jim are a young married couple with financial troubles. They want to get each other the perfect Christmas gift but have no money to do so.
Della has beautiful long hair, which she cuts and sells to buy Jim a platinum chain for his pocket watch. Jim, meanwhile, has sold his pocket watch to buy Della some beautiful combs for her long hair.
When they find out what the other did, they put their gifts away and enjoy Christmas dinner together, celebrating what may be the greatest gift of all: their love.