not just the fact that each could not use their presents, but the reason they could not use them: they each sacrificed all they had for the happiness of the other YET could not make use of the actual object
all they really had at the end of the story was the absolute knowledge that their lover was willing to sacrifice all they had for the other's happiness
and that was a better gift than any gift could be, SO they now had nothing, yet they had everything.
It was christmas. Although they had decided not to exchange presents , each wanted to give the other a gift. Jim sold his watch so that he could buy combs for Della to wear in her beautiful long hair. Della cut her hail and sold it so that she could buy a fob chain for Jim's pocket watch. As they exchanged the gifts , they came to know the price they had paid for the gifts by sacrificing which was most dear to them, They realised what they had given up in order to show their love for each other.