I think the root of the connection between ENFP and INTJ is the intuition. ENFP has dominant extroverted intuition, and INTJ has introverted intuition, and these two functions allow access to each other. The extroverted intuition of the ENFP can "see into" the INTJ's introverted intuition and vice versa, so the two kind of complete each other. It allows each person to have a more complete kind of intuition. The INTJ helps the ENFP to see into themselves and the ENFP helps the INTJ see into other people.
ENFPs also have much more ability to "go with the flow" than INTJs. Therefore, the ENFP is like a natural antidote to the INTJ tendency to be overly serious and judgmental. This is a P/J difference.
The INTJ helps the ENFP organize their external environment. I am always helping my ENFP friend find his keys, wallet, or cell phone
It's all about sharing the same basic perceiving function, intuition, but having the other dimensions be different.
ENFPs also have much more ability to "go with the flow" than INTJs. Therefore, the ENFP is like a natural antidote to the INTJ tendency to be overly serious and judgmental. This is a P/J difference.
The INTJ helps the ENFP organize their external environment. I am always helping my ENFP friend find his keys, wallet, or cell phone

It's all about sharing the same basic perceiving function, intuition, but having the other dimensions be different.