Answer:
Unhappy people are never satisfied.
Step-by-step explanation:
According to the given excerpt from "The Necklace", there's a conversation between two people who I assume to be a couple. From their discussion, the man got her a piece of clothing that he went to great trouble to get so she could wear it for a party but she was not pleased and spoke angrily to him.
Based on this, the theme that it likely supports is that unhappy people are never satisfied.