The excerpt from Portrait of an INTJ really hit me when I first read it.My INTP female friend is golden with expressing herself when people stop talking and just listen to her.It is not easy for the INTJ to express their internal images, insights, and abstractions. The internal form of the INTJ's thoughts and concepts is highly individualized, and is not readily translatable into a form that others will understand. However, the INTJ is driven to translate their ideas into a plan or system that is usually readily explainable, rather than to do a direct translation of their thoughts. They usually don't see the value of a direct transaction, and will also have difficulty expressing their ideas, which are non-linear.
I really feel like I have so many amusing smartass one-liners from linking ideas/situations/thoughts in my head that I just can't "translate" into words in time to spit them out for "witty repartee" to make sense. (I also tend to mumble, which makes it worse.)
But I find that typing is the place for me. It's like the "optimal speed" for my brain to translate my ideas and get them down so I can move on to the next idea.
Speaking is difficult (I have to go slowly if it's a real deep thought) and handwriting takes too much time; my brain moves faster and I lose things. But typing is where I find the happy medium. (at roughly 60 wpm)