I think we can actually be pretty good at instinctively knowing where our needs are being met and knowing what we want- but there's a weird thing that happens when we're directly asked or expected to articulate it. Because for us, it's a kind of 'knowing' that couldn't be further from something that's easily put into words. At least for me, in the past, when I've tried articulating wants/needs on the fly (to explain to someone why I declined going to the movies, or going to dinner with a group of people, why I wanted or didn't want to do this or that, etc)- it has often been a matter of me coming up with the easiest answer that comes to mind, for the other person's sake. It's only after repeated experiences with someone that I'll discern whether it's a good idea to give the most accurate answer I can- depending on how they react, it becomes clear whether they are helpful to bounce reality off of in order to understand it/myself better, or whether I should give them the cordial 'short answer' without giving them much access to what's actually going on. And as I get older I've become aware the consequence of doing too much of the latter can actually make me lose touch with the wants/needs that are genuinely there. Discussing my wants/needs with someone who doesn't understand can actually make me lose touch with my wants/needs.
This is kind of parallel to something you wrote- about how others' reactions can influence what I think about the answer I give- there's something about articulating wants/needs to someone who won't understand that actually pollutes the process and takes me further away from the truth. And all of this is actually such an instinctive process that I couldn't make a conscious decision to trust the latter with more access to my thinking process if I tried- that part of my mind just shuts down around people who clearly don't understand me. I don't even have access to it myself in their presence. But around those whom consistently prove useful- bouncing reality off of them results in me having a better understanding of my wants/needs, rather than feeling more confused about it- there's just a feeling of 'knowing' it's correct because I feel truly seen/understood.
tl;dr: I agree that we can have a hard time seeing our wants/needs in real time- that consciously, such things often only feel 'accurate' in hindsight- but I think as we get older the hindsights we've had accumulate and manifest in a strong unconscious pull that we do feel in real time. We may not immediately understand it- but it's there, it's strong and it's in real time. Also, I've noticed confusion about that 'pull' is exacerbated by interacting with people who don't particularly understand where I'm coming from.