Normal disclaimer that I am basing the following on a successful pairing but individual mileage may vary.
When it’s working
– What are the joys and positive aspects of these relationships?
The concept of a mindmate is strong here. Together, we prefer Thinking and Intuition as our primary methods of decision making and information gathering/experience. We prefer and do our best seeing the world this way and it allows us to come at problems from different processes, but from understandable and easily agreeable end points. There is both novelty and understanding.
- How compatible do you think these two types are in general?
As compatible as any other well adjusted individuals would be.
- Why are they attracted to each other?
From a typological perspective, there's the mindmate scenario described above, where there is enough novelty to keep the dynamic interesting but enough familiarity to not infuriate or get in the way.
The difference in energy levels is an attraction too: INTPs can suffer from lack of purpose that the ENTJ will probably have too much of, while the ENTJ can burn themselves out and sometimes just needs to fucking relax. INTPs are uncomfortably aware of the fact that there is really no objective reason to do anything at all, so Enter the Dragon (ENTJ) with their vision and enthusiasm.
From a specifically human attraction perspective, she's a hot, exotic woman from a foreign land that speaks a funny language that I find intoxicating, and I am the Platonic Form of Americana distilled in to a sexy bag of meat, bone, and synapses.
- How to they compliment each other?
Again, we both prefer thinking and intuition when examining the world and making decisions together. We both can downplay emotional decision making, but it's unlikely that BOTH of us are in the grips of our inferior at the same time, so when our thinking can sink in to our lower functions, the other can point this out and be the perspective check either of us need to collect ourselves and use our better tools. Also, there's a comraderie in being F-tards together and there's no power dynamic where one of us is "more skilled" than the other in a particular typological domain.
- How well do they understand each other and why?
"Understanding" can be difficult at times, since our thinking makes sense when plotted and charted and explained, but we would never actually think that way naturally ourselves. This is a blind spot that I think will come with time. Already it's easier for me to inhabit her thinking and make decisions based on her criteria and I would assume vice versa.
As far as we understand each other's desires, motivations, likes/dislikes, kinks, etc; that comes from being open and honest without judgment with each other, which we're equipped to do.
- What are they like together raising children?
We will find out soon.
When it’s not working
– What are the challenges when two people of this type are in a relationship?
The balance may be upset between accomplishment, energy, and pace. The INTP can be strung out and tired at the energy required to Make Things Happen and the ENTJ can get understimulated and/or bored if there's nothing to do. The INTP will want lots of alone time and the ENTJ will want help and participation.
Emotional concerns can go unnoticed for long periods of time because both types will "not deal with things" and save them for later. For the INTP, they'll internalize, distance, become less present and eventually lose it at something minor, resulting in a Fe-ruption. The ENTJ will start hyper controlling the environment while simultaneously being extremely sensitive.
Both of us are very future oriented so we can often lose sight of the now and forget to take care of our selves.
- What are some of the communication challenges they can have?
INTPs are less detail oriented and will assume flexibility even when something is specific. Like, be there at 12:30? More like 12:30 ish. Shit happens.
ENTJs are actually extremely clear communicators so I will admit miscommunication is usually my fault, hah.
- What are the biggest frustrations between these two types?
Probably the concept of flexibility and structure. We'll each define it differently and want our own versions of it. I'm getting really bored of doing this so the rest of my answers are going to be really shitty, also because there aren't too many negatives at this point.
- How can they take each other for granted?
Lack of understanding and respect for the other's process and why it's important to them psychologically.
Advice for couples
– What recommendations do you have?
ENTJ- Relax and don't be so sensitive.
INTP-Be more present and don't hold back.
