This is obviously not Enneagram, but AhsokaTano323 requested it and I'm happy to explain as much as I know, which isn't very much, but I'll try.

There are 8 cognitive functions; the first I'm explaining is Ni:

Ni - Introverted Intuition:

The dominant function of INxJs, Ni is paired with Se, Extraverted Sensing (which I will get to later). For example, INTJs have Ni dominant and Se inferior. 

Introverted intuition basically means an individual can predict their own path forward: What I want to do, What I intend, What I desire, What I'm going for, What my goal is, etc. It's all about knowing what you want, more future based, like What I want to get later. 

It allows you to stay focused on your goal, or what you want to do. It's sort of the luck cognitive function.

It's about finding the one best path forward, optimising success by finding the single path forward. It's getting somewhere, not exploring all the possiblities, but focusing one just one. (I thought I might be INTJ, but this cleared it up for me, as I do not ever focus on one thing.)

INTJs and INFJs have Ni as their dominant function, or Hero function. This means it is about knowing what they want, following goals, etc.

ENTJs and ENFJs have Ni as auxiliary, or Parent function, which means they are responsible about what they want, about their goals, desires, where they're going.

ISTPs and ISFPs have Ni as tertiary, or Child function, which means it can get through any obstacle without much trouble.

ESTPs and ESFPs have Ni as inferior, which is the "insecure" function. Ni inferior will mean they are insecure and afraid about what they want.

Introverted intuitors, because they have Se in their function stack, have to have the freedom of decision. They cannot stand having no freedom. Mostly with types that have Se dominant or auxiliary, or even tertiary function.

If Ni was an element, it would be fire, because it's about wanting what you desire; about being very precise; burning (ignoring) everything in the way to get to your goal.

[Source: &t=92s]