As I've said before, I'm an ISFJ.
This means that my fourth and least developed function is Extroverted Intuition. The websites I've read have said that as such, our intuition can steer us wrong. Joe Butt says, "ISFJs are easily undone by Extraverted iNtuition, their inferior function" (Humanmetrics.com: ISFJ).
Now, that's my weakest function. That's what I'm bad at. My intuition is a funny thing, and I'm only vaguely conscious of it. Sometimes I'm not sure if what I'm listening to is my extroverted intuition or my women's intuition, or something else entirely.
There are times when my intuition is spot on, and there are other times when I can't trust it. Is that all in my head? Do they actually not like me? I'll walk around with an uncomfortable feeling, it isn't right, how can we regain peace? Then I turn to prayer.
Sometimes I'll think of something to say in a situation and then I'll get a feeling: don't say that. If I do say it, sometimes I regret it, sometimes not.
One time though, a friend told me that he couldn't meet me as planned, his parent's wanted to talk to him about something. I could easily explain it away as not a big deal, but my gut wouldn't accept that. Whenever I thought about it, I began to shake. My legs trembled. I felt cold and my heart felt strange. The fear overwhelmed me, I could logically explain it away and make sense of it in my head and come up with some non-dire explanation. But I couldn't accept that. It turned out my intuition was correct. My friend admitted that something was wrong, and agreed to tell me in a few days. During those few days of anxious waiting, my brain pondered and I figured out what had happened ahead of time. I was calm when the blow fell. I felt almost nothing, my heart was a lump of dead flesh. Now, on Funky MBTI Fiction I read that the fourth and weakest function "often only turns up under extreme stress or anxiety." This was a case of extreme stress and anxiety and this issue that my intuition cued in on was not the only anxiety I was facing at the time. I remember hunching up in a boxed in corner of my bedroom sobbing on the phone to my best friend...
Another facet of having extroverted intuition as the fourth from your longest and strongest suite (to use a bridge term) is not always knowing what to say to people or being able to understand their meaning. ISFJs "aren't quite as good at reading others as their extroverted counterpart. The ISFJ needs external indicators to understand what is required from them and can sometimes get wrapped up in their own internal world and forget to check their Ne." (ESFJ vs. ISFJ)As a side note on this: it also really stinks when you realize your world in your head isn't real, and the characters in your story aren't quite so pure and noble as you thought they were.... This has happened to me, and it seems to have also happened to Dr. John Watson (aslo an ISFJ) in BBC's Sherlock,
When I'm in a conversation usually, feelings of warmth and support are there, but they stumble out of my mouth in awkward words, too deep, not deep enough, not quite what I meant to say or how I wanted it to sound. Or I keep quiet out of fear of saying the wrong thing. Later, my brain catches up to my heart and I think of a much better way to say it. (Guess why I like writing?)
I really don't understand my fourth function, I'm just trying to give some examples of what it's like to have extroverted intuition as your weakest function. Try performing brain surgery on yourself...it's like that...