I've frequently seen people reference Lenore Thomson's definitions of Fe, and I feel that I need to clarify something (as Fe is want to do). Lenore Thomson is self assessed INTJ, and from what I've read of her work, I would agree. She's a brilliant INTJ with an amazing amount of insight about cognitive function theory. However, as an INTJ, she has no native understanding of Fe, and therefore can only understand it as an external concept through her observations, and furthermore her filters of Te and Fi. This leaves her in a position where her understanding of Fe comes only from observing Fe in others, usually SFJs, and therefore her descriptions of Fe are not entirely well defined and rather biased as an outsider.
Therefore, I feel compelled to clear up some misconceptions about Fe.
Fe is at its core a system of reasoning based on how it feels things should or should not be.
Let's analyze this statement. Fe is at its core a system of reasoning - meaning that it is in fact a process of analysis, deduction, and assertion. Based on how it feels - denoting an emotional, philosophical, and ideological bias. Things - external concepts, people, places, systems, etc. Should or should not be - denoting an expression and assertion of expectations.
Combine all of these factors, and you now understand Fe. Values and judgments applied to the outer world.
However, all of these factors create very common behaviors. Fe users often have a great deal of emotional investment in people, even strangers. Fe users often have a great deal of expectation in social arenas and emotional interaction. Fe users often engage in what could be called emotional currency. All of these behaviors are the result of Fe being applied to these situations, not Fe itself. This is such an important distinction to make for people who are not native Fe users. Fe is not the sum of its expressions because its expressions are half Fe half situation, and most importantly not all Fe users have the same expressions of Fe.
For example, a stereotypical Fe dominant would use their Fe to adapt to others and create harmony - because they feel that's how things should be. However, another Fe user could just as easily create conflict with others because they feel that the others are not doing things the way they should be done. This proves that Fe is not the 'get along' function so much as the assertion of values function. Fe users often prefer harmony, because they often feel that harmony should exist not because Fe inherently seeks harmony. Fe inherently seeks to exert the individual's values with respect to the external.
A classic example of this is how obnoxious some ENTPs and ESTPs can be because their inferior Fe feels things should be a certain way, as led by how their Ti understands things to work. I've known several ENTPs and ESTPs who very much felt that harmony was a waste of time. However, this is still a manifestation of Fe.
Therefore, as much as Fi is a function of one's internal values. Fe is a function of one's external values. This is evidenced by the fact that most Fe users know exactly how they feel about things, but are often unable to discern how they feel inside. Fe users have strong opinions, but are often a mystery to themselves - assuming they bother to question their own feelings (Fi) because Fe tells them how they should feel. An Fe user can convince themselves that they should feel things or in ways that they simply cannot, and this can cause a great deal of internal emotional conflict. On the other hand, an Fe user can convince themselves that they should feel something and thus be motivated to greatness. For example an ESTP who convinces themselves that they should be tough, fearless, etc. or an ESFJ who convinces themselves that they should be benevolent, kind, and patient. In both cases the individual is applying an external ideal to themselves, and is thus using Fe rather than Fi.
The idea that Fe is inherently based on how others feel is incorrect. Fe can be swayed by the opinions of others, but it is just as capable of bolstering itself against the opinions of others. What matters is whether or not the Fe user feels they should be swayed by the others in question. For example, a religious Fe user would likely feel that they should adapt their views to match their religion, but would not at all feel compelled to adapt their views to match another religion when around people of a different faith. This person may feel compelled to be polite and harmonious, and therefore respect the other faith's right to its traditions, but would feel strongly that they should not also practice while in the presence of it. However, an Fe user who feels antagonistic to another faith might well be disruptive if they felt this was what should be done. Fe is one of the biggest reasons for religious clashes. Clearly, Fe users in wars of ideology are not feeling compelled to be harmonious. In fact, some of the most heated arguments come from two Fe users who have differing views on how things should be.
Therefore, while Fe is usually motivated to be harmonious, and many other things attributed to it, because it is a function of external values, it must be noted that Fe is simply that - a function of external values, and as such it is much more diverse and applicable than most definitions give it credit.