"It isn't fair."

Ask someone to what "it" refers, and they'll generally be shocked by the notion that their words should have referents. When the shock wears off, it will be that "the situation" is unfair, which is a category error. The state of the universe is unfair? Is gravity unfair too? How about the fact that it rained yesterday?

Fairness is a quality of a moral being or rules enforced by moral beings. But there is rarely any particular unfair being or rule enforced by beings behind "it isn't fair".

"It isn't fair" empirically means "I don't like it and I approve of and support taking something out of someone's hide to quell my discomfort."