It is easy to confuse the two because they have have a number of similarities. For example:
1. they are both information gathering functions.
2. Like all information gathering functions, they are both involuntary – that is they both gather information on their own, you have little control over what you learn from them once you enter an environment except avoiding bad environments.
3. They deal with abstractions – unseeable and untouchable connections and behavior of things. Fourth, since they are irrational, they are not normally what people defining themselves with.
4. Like all information gathering functions, they are both liable to pickup stupid ideas.
Now to differences.
Fast vs focused
Let us say we give people with a subject or problem of their interest and ask them to come up with insights on it. Now, this subject itself we will call ‘inspiration’.
A person with strong extroverted intuition (Ne) is someone who operate really fast at outside levels (extroverted). You hand them a problem or subject of their interest, they will spend some time – a few minutes to maximum a few months with it and coming up with insights about it. They will go on doing so until they are distracted by some new subject. Ne is like a flame that burns big but for a short while once it is inflamed by an inspiration. It needs a new inspiration every once in a while. It is somewhat infantile in the way it can so easily get bored quickly and has radiant but quick-burning energy. Ne works best where knowledge of different sciences is to be brought together – this is because a mature Ne user will already have worked on a number of projects that relate to different kind of fields and learned something from it by time he takes the next one. Ne users are thus good at system development, arts and social sciences where different new projects have to be dealt with.
Introverted Intuition is slow, steady, and more focused. People with Ni as one of their leading functions will be more focused and detail-oriented. This is because the subject won’t bore them that quickly. They are in fact perfectly capable of working themselves to death. If they work long enough with an idea that Ne dominants were too lazy to care about for long, they are capable of some awe-inspiring and even groundbreaking observations. Unlike Ne dominants, their extreme focus means they will struggle to keep up a number of pursuits at the same time. Thus they work best knowledge of fewer fields but a lot of it is needed — sciences, programing and medicine for example.
Time Versus Space
Another way of looking at it is that Ni picks patterns over a long time while Ne picks patterns over over a large space. Ni picks patterns from information it sees over a long period of time in a small field – giving it mastery over the field. Ne picks relatively superficial information in a large field for very quickly.
Self-awareness Vs Confidence
Another difference is Ne works at a more conscious level – a strong Ne gives you the source of its ideas and can explain them perfectly. Ni’s ideas, on the other hand, show little awareness about themselves. The ideas from Ni often come as hunches, gut feelings, whispers from God, etc. It is because Ni has been with the problem for a long time and can’t tell what gave it the idea. Ni’s lack of knowledge of its nature doesn’t lessen the confidence of XNXJ, rather it inspires in them a blind confidence and often inspires the same in others. Thus a person with a strong Ni will be a judging type.
It is Ne who will have more doubts about his or her observations as they haven’t spent as much time with problem- this making a person with Ne as a dominant or auxiliary function a prospecting type. The good side of this prospecting nature is that Ne are more likely to stay open minded and correct their behavior.
Security Versus desire for adventure
A person with a strong Ni has a need of a secured, a planned environment where it is left entirely free to work on a project of its interest. Distractions, things that can’t be trusted to fit known patterns scare Ni dominants. A person with a strong Ne doesn’t need that kind of secure environment, in fact, it will feel starved for new distractions if it is forced to follow a disciplined routine — rather it grows out in wild and seeks strange and weird.
Productivity versus Originality
As a last point, when Ne is one of first two functions in someone’s stack, the other is Ti and Fi which are both introverted information organising functions – making the individual very individualistic. It is because they organize information based on how a thing will affect oneself or a given individual rather than the impact on everyone. Fi studies how things affect the person themself while Ti studies how things appear to the person themself. Since these functions individualistic, they can be original more easily but less productive (as far as goals of common good are concerned) in everyday life.
Ni works with Te and Fe which are both extroverted information gathering functions which means they both organize information based on the relationship of a thing with everyone. Fe studies how a thing affects everyone in general, Te studies how a thing appears to everyone in general. This makes the individual far more productive in everyday life but very rarely exceptionally original.