As a fellow 4:
Take some time to yourself. Forget your obligations to society and the expectations they have. That includes family and friends. Tell them that you'll be busy a while. Take the time to self-reflect. They'll understand.
Then: Read. Think. Read. Think.
Roughly translated: take personality tests, read up on enneagram 4, read up on INFPs, read this forum for that matter, to see which types interact how with everyone.
Next..process. Let all that info go through your mind, make patterns, compare it to what goes on in your real life, and see the big picture. Think about what intrigues you, what matters to you.
Lastly: Judge. Bounce all of that off of your Fi. You know how when you think of something and you close your eyes, you can *feel* by the warm glow near your heart (yes, I'm aware of the mushy factor but it does really work like this), if it *feels* right? Don't *ever* question that feeling. That, right there, is who you are. If you get thoughts about 'what about this, and how will people think about that!', do NOT question the rightness of your judgement. What you *can* do, is refine the question you asked your Fi. Think about things, mull it over, and rephrase. Finetune. Find out what *exactly* in that original phrasing your Fi was responding to. And what was causing the conflict with your mind. Sometimes it'll be your fears, or the social ettiquette you were taught that gives that backchatter from your brain. Other times, it's because you haven't refined the value enough and it's entertwined with another value. Seperate the two.
For example: I have the value that I like seeing people happy..so I try to please them. However, I also have the value that I want to be my unique person and only do what feels right to me. They clash often. Take each situation apart and see which one is actually valid in that particular situation and which one ranks higher. Don't let them get in each others way. They both have merit.
Another good thing to do is reminisce about the things you react strongly to. Figure out *why* that is. Usually there's either a strong value there that you aren't conscious of, or, you've been hurt/scared/traumatized by a previous event. If the former, find a way to tweak it so you can respond properly to that value, if the latter, mull it over and analyze the situation, so you know how to respond without overreacting to it the next time.
After all of this, you'll probably have a *ton* more questions. So press repeat. Read once more, to gain answers, to process and to figure out who *you* are and what is important to *you*
One more thing: other people are interesting to spark your imagination, to learn from, to enrich your own pov. But don't EVER let another person tell you who you are. Part of being a 4 is carving out your own unique path. And even more: you should do so. You're entitled to. No, it's not selfish. It can appear selfish if poorly executed, is all. Refine your methods..don't suppress who you are though
Good luck!
Edit:
Specifically geared towards dealing with Envy:
I personally hold dear to see people happy. I use that value to disable envy. Or rather, turn it less poisonous. The second I feel envious about something, I disable it, coz I hate feeling that way. And I do so, by reminding myself to look at those people instead of myself. It's great to see them that happy with what they have, that they were so fortunate to have [Insert thing I'm envious of] in their lives. And I use their example to find inspiration for myself on how to obtain it and finetune it so it's what *I* need. Often, getting what they have is not perfect for me. I need the me-version. And they spark ideas on how to get there
As said before, if you feel strongly about certain things, be curious about yourself. Wonder *why* that is. Why is it that makes you feel so strongly. And see if perhaps you can finetune the feeling, the reason, and the reaction. It'll help you adapt your responses to become the person you wanna be. Ask yourself, if you saw this response in someone else to that particular situation, if you could understand it and find it appropriate. It'll help you gauge what you would ideally like to be like. Don't beat yourself up if you aren't able to adjust it immediately, keep going over it, finetuning it, you'll get there eventually
