Their motivation was the desire to study people and how they work based on what they think. People are interpersonal systems to an INTJ, again, another system for the system builder :)

I thought this was interesting. I’ve been working lately on trying to figure out INTJs. Actually, more specifically, the INTJs in my life.

The INTJ way & INFP connection

INTJ

Yeah. I deleted my last post about not knowing his type because I figured it out. You may not agree, but it totally fits. He’s perhaps more diplomatic than many T’s I know, and probably borderline on the J/P.

• Introversion: As pointed out before, shy, withdrawn, enjoys spending a lot of time alone. Suggestion that social environments are taxing for him.
• iNtuition: Speaks in broad terms. When describing or explaining something, talks generally rather than giving a lot of specific details. Interested in the abstract rather than the concrete.
• Thinker: Values knowledge, intelligence, logical thought. Not offended or intimidated by conflict/criticism. 
• Judger: Finishes what he starts with apparent ease. Seems to value the product, as well as the process. His creativity is always put to practical use — an idea is not just an idea, but something that can be implemented on the world around him.

INTJs:
- Live in a world of ideas and strategic planning
- Usually self-confident
- Generally extremely intelligent and capable
- Good listeners
- Tendency to believe they’re always right
- Observers, skeptical
- Perfectionists: Still spends months drawing a single episode of Family Guy, because “that’s the only way to do it”, according to him.
- Have an unusual independence of mind, freeing the INTJ from the restraints of authority, convention, or sentiment for its own sake.

Self-confidence often mistook for arrogance:

“To outsiders, INTJs may appear to project an aura of “definiteness”, of self-confidence. This self-confidence, sometimes mistaken for simple arrogance by the less decisive, is actually of a very specific rather than general nature; its source lies in the specialized knowledge systems that most INTJs start building at an early age. When it comes to their own areas of expertise — and INTJs can have several — they will be able to tell you almost immediately whether or not they can help you, and if so, how. INTJs know what they know, and perhaps still more importantly, they know what they don’t know.”

- http://www.typelogic.com/intj.html

Though I believe it’s possible SM is borderline on the J and P, upon reading several biographies and articles/interviews, his life, though perhaps sometimes a little disorganized, is always on track and always has been. He finishes what he starts, refines his existing skills and successfully juggles several projects at once. This, to me, seems the lifestyle a J would be quicker to chose for themselves (and quicker to handle) than a P.

Also: One important difference between INTPs and INTJs,

INTP: Perfectionists of thought
INTJ: Perfectionists of action

INTJs have a strong desire to implement change in the world around them where they believe improvement is needed. This constant quest for improvement can be annoying to other types, particularly those who believe the system doesn’t need changing.

This article http://www.forbes.com/forbes/2012/0604/celebrity-100-12-family-guy-seth-macfarlane-gets-serious.html 

* Particularly 7 paragraphs down, the section discussing his concern for science.

Read that and tell me he’s not an INTJ.

http://intjcentral.com/intj-vs-intp/
- This website explains it nicely.

Has a good description of the difference between P and J.

“Misunderstanding the difference between J/P is one reason many people mistype.”

Also a great website for INTJs.