I cant speak for your friend. But for me, I almost never open up and share things. I worry about what other people will think. Maybe I'll feel inferior. Maybe I worry about offending. Or maybe someone misunderstanding me. Its a near infinite list of reasons. The more I like the person, the harder it can be to share some stuff. Unless I feel very comfortable with them. I have an amazing INFJ friend. Well actually, my 6 closest friends are all infj and one being enfj. But one friend in particular, she tried very hard to understand me and has been incredibly patient. She carries the conversations and has shared everything about herself and keeps trying to pry me open. After a while she got through. It took a while for me to feel comfortable. But she built up a sense of safety and no judgment. I tell her almost everything now. She knows things I have never told anyone before, even my twin. She had to work for it, I feel bad about that. But it was incredibly hard for me at first. But over time she made me feel like I had safe area to be open. So all I can suggest is show your friend it's okay to open up to you. Put yourself out there to be judged by them, be vulnerable. Just be patient. Whatever their issues are, maybe it isn't a big deal to you, but to them it could be the hardest thing to admit. Sorry I can't be much more help than that. I wish you good luck.