Something to note about the descriptions of Fi, and especially Fe...
Most of the 'research' done on these two functions comes through the filter of S types, which skews the perspective for these functions toward Se and Si.
The NFP population is roughly 10%, so there is a fair amount of Fi input when paired with Ne, but most Fi dominant (and secondary) users are SFPs. Keep that in mind when considering the descriptions of Fi. There is usually a bias toward Se thinking when it is presented, but from what I've read Fi is fairly well represented as a unique function unto itself.
However, the NFJ population is less than 2%, while the SFJ population is close to 25%. The vast majority of input on the subject of Fe comes from Si users. The notions that Fe tends toward politenesses, social contract, and emotional currency come from this pairing of Fe with Si - which is a very 'conventional' function. Si likes tradtion, repitition, and rote. For an Si user, Fe manifests through such practices.
However, Ni users are nearly the exact opposite. We have little use for tradtion, repitition, and rote. We see the hidden patterns, focus on the unknown, and are looking to the future so intently we often fail to notice the present. Ni and Fe users do not focus nearly as heavily on social ritual as we do the actual needs of other individuals.
For example, SFJs prefer to engage in "Good morning, <person's name>. How are you today?" "I am fine. How are you, <person's name>?" "very good, thank you (even if they're not). How did <remembered detail that was of concern to the person they're talking to> go?" "Quite well, thank you. How is <returned detail of concern to the person they're talking to> going?" etc. The SFJs are showing concern for one another by walking through an expected social rote, asking about details of concern to the person they are speaking to show that they care (this is an example of social currency), while minimizing (or outright denying) their own hardships so as to not upset others.
Meanwhile, NFJs tend to prefer to handle the same situation differently. Before any words are exchanged, the NFJs are reading each other for the answers to the following - How is the other person feeling? Are they alright? Is there anything to be concerned about? Are they busy? What is the best way to approach them at this moment? We're amazingly adept at detecting these things in others, and in exponential proportion to how well we know the person in question. Once we determine this, our social interaction follows suit, but is always situational to the factors we've determined. For example, if we determine someone is busy, we smile at them and leave them to their attention. If we see that someone is in need of warmth, we show it to them in as sincere a way as we can, which only includes social conventions when we know that person needs them.
Fe's motivations are the same - concern for and caring about others -, regardless if it is paired with Si or Ni. However, it manifests very differently because of the perspectives of Si or Ni.
But, there is another aspect to Fe that is lost in most of the descriptions I've read...
More than a concern for others, which is just a side effect, the true nature of Fe is that Fe is philosophical reasoning. (While Fi is abstract reasoning.)
Fe is right brained reasoning, with an external focus. (Where Fi is right brained reasoning with an internal focus.)
Fe is the clear sense of knowing how you feel things should be, and what others want. Fe feels that this should be this way, and that should be that way. (Fi is a clear sense of how you feel you should be, and what you want for yourself.)
Fe is the sense of right and wrong. (Where as Fi is the sense of good and bad.)