I think internally I'm more of a 4w5, but my actual behavior is very 9w1. I'm also an ISFP.
Someone on reddit asked me to post my fears:
"Not entirely sure, but I think these:
Being attacked in any shape or form.
I tend to be careful and polite a lot around people (so I don't trigger them), and share my thoughts, interests and opinions only to those I'm close with (so the wrong people can't mock, attack or make fun of them), and even then I can be quite selective. I also tend to avoid conflict and hide my anger, even if I get very angry (because they might also be angry and they could be way more vocal and upfront about it than I am, and that could escalate it), I will usually just keep it to myself and just have negative, aggressive thoughts aimed at them.
I'm somewhat afraid to act "out of character", basically do and say things people normally wouldn't expect of me. Not sure why, though."
He then said I was likely a 9w1. I do relate to the actual behavior of a 9w1 (I also tend to adapt to the person I'm talking to, like a chameleon, which seems to be a 9 trait also), like I described above. However, I also really relate to 4 (and 4w5 as an extension).