The second component of NVC is "to express how we are feeling." Before we express our feelings, we must be aware of them. It can be very tempting to ignore our feelings and just let our feelings fuel our actions without reflection.
NVC can help us become aware of our feelings and strengthen our feelings vocabulary. This will produce benefits in both intimate and professional settings. "Expressing our vulnerability can help resolve conflicts."
Everyday language often treats things that are not feelings as if they were. For example, "I feel it is useless." This sentence actually expresses the speaker's opinion, what she thinks, rather than what she feels. Usually when this is the case, the word "feel" can be replaced by the word "think" without changing the meaning of the sentence. Or "feel" may express our interpretation of the actions or opinions of others, as in "I feel ignored." Expressing such "non-feeling" feelings does not fulfill the second component. It does not express the vulnerability or offer the connection, and may sometimes be seen as an accusation, as in "I feel you have neglected me" or "I feel neglected."
Rosenberg gives a long list of feeling words. Not sure why.
Language is funny. "I am sad." NVC is okay with that, but maybe general semantics and cognitive behavioural therapy would criticize it as too static, as if sadness was a permanent part of my identity. "I feel sad" gets a thumbs up from those two, but Rosenberg is less happy with it, though I suppose he will let it slide. English needs a better verb for expressing the idea that "I am experiencing sadness." Spanish has 2 versions of the verb "to be", as I recall the major difference between them is that one is used to describe permanent things ("I am a human being") and the other for temporary states ("I am at home"). And Orwell recommends that we do away with the passive voice in our writing. Now I am babbling. "Feel" is a nice active verb, but has the flaw that you can feel things that are not really feelings.