Emotion Differentiation
Emotion differentiation is how finely a person carves up their own feelings. Someone low in it feels bad. Someone high in it notices that this particular bad is disappointment rather than resentment, and that the two ask for different responses. It is also called emotional granularity, and it is the assumption sitting underneath every "put a precise name on it" instruction in wellness writing. The awkward part is that when researchers looked at people's natural language, a richer vocabulary for bad feelings went with worse mental health, not better.
What it is
Two people leave the same appraisal meeting. One says it was awful. The other says they were embarrassed about the first half and quietly relieved about the second. The second description contains information the first does not, and the standard claim is that having that information available makes the feeling easier to act on. Disappointment asks for something different from resentment, so knowing which one you have got is practically useful.
The construct is conventionally traced to Lisa Feldman Barrett's work on emotional granularity around 2001. That origin is recorded here at medium confidence, because this vault has not opened that source, and the evidence on this page rests on a much more recent study.