Isn't a person acting to fulfill one's duty something they do because they feel it is in their best interest? I would not be using the term "happiness", rather

Isn't a person acting to fulfill one's duty something they do because they feel it is in their best interest? I would not be using the term "happiness", rather say that a person acts to remove a felt uneasiness. How do you define "happiness"? What do you propose as an alternative to the subjective theory of value? (edit: if you disagree with it, I noticed it was the other guy hinting at being against it.)