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This partially answers your question
In response to both questions I have definitely noticed this! I have talked to my ENTP friends and they both agreed they do no get along with ENTJs. They make them uneasy.
It is quite hard for me to describe why I cannot get along with INFPs. I know three (two female, one male) And while we can communicate fairly well, our opinions are almost opposite on the topic in question. For example, we both think we "get it" when talking about a philosophic issue. When can never come to a consensus. I can only agree with people who have the Fe function. I tend to use it as a means to and end to fit into the framework. The Fe thinks about the situation as it applies to others where the Fi sees it applying to themselves as an end in itself. I have heard an INFP utter those same words when arguing about something. Since this is their dominant function and I do not understand it, we usually do not get along too well. There is this unacknowledged friction. We should just agree to disagree once and for all but we end up arguing too often for my liking. Since both of our types don't like conflict we don't usually end up being friends.
Although INFPs share the same first three letters, our functions are opposites in regard to them being either extroverted or introverted.
The way we use our functions are opposite, which all has to do with the P and J.
I think INFJs would get along better with INTJs because they have Introverted Intuition as a dominant function. They are supported by different yet still extroverted functions (Fe and Te). I think they complement each other well. I think you tend to get along with those that have functions in common with you.
I'd be interested in hearing about why you think so...perhaps some personal examples?
This partially answers your question
This is mostly accurate...
INFP and INFJ typically do NOT get along well, in my experience.
I have one band with 5 people where 4 of us each represent one of the four xNxP types, and then the fifth guy is INFJ...so he's already at odds with our perspectives on that point.
Nonetheless, he tends to get along ok with all of us except the INFP! They clash like hell.
The key difference, I think, is that the INFP's Fi views ethics as an end unto itself...INFPs wish to possess the most internally consistent ethical viewpoint because that is the end goal.
INFJ's Ni views ethics as a means to an end, though, and INFPs find that disingenuous and rather disturbing. (In truth, INFJ's dominant Ni makes him much more similar to an INTJ than to an INFP...note how well INTJ and INFJ tend to see eye to eye, but this is not true of INFJ/INFP or of INTJ/INTP. Another example of J/P being the biggest difference!)
I find that the type that shares your first three letters but not the last one tends to be one of the hardest to get along with in general...has anyone else noticed that?
In response to both questions I have definitely noticed this! I have talked to my ENTP friends and they both agreed they do no get along with ENTJs. They make them uneasy.
It is quite hard for me to describe why I cannot get along with INFPs. I know three (two female, one male) And while we can communicate fairly well, our opinions are almost opposite on the topic in question. For example, we both think we "get it" when talking about a philosophic issue. When can never come to a consensus. I can only agree with people who have the Fe function. I tend to use it as a means to and end to fit into the framework. The Fe thinks about the situation as it applies to others where the Fi sees it applying to themselves as an end in itself. I have heard an INFP utter those same words when arguing about something. Since this is their dominant function and I do not understand it, we usually do not get along too well. There is this unacknowledged friction. We should just agree to disagree once and for all but we end up arguing too often for my liking. Since both of our types don't like conflict we don't usually end up being friends.
Although INFPs share the same first three letters, our functions are opposites in regard to them being either extroverted or introverted.
The way we use our functions are opposite, which all has to do with the P and J.
I think INFJs would get along better with INTJs because they have Introverted Intuition as a dominant function. They are supported by different yet still extroverted functions (Fe and Te). I think they complement each other well. I think you tend to get along with those that have functions in common with you.