Know thyself? Not so sure about that.
I'm not completely convinced that anyone really knows themself. I think we like to think each person understands themselves better than anyone else, but I don't think we can ever truly say we "know" outselves, because I don't really think that there's anything truly to know. There's no real objectivity in self-knowledge, only what we perceive to be true, and across almost every artistic medium, we see the notion that whatever we believe to be true about ourselves can be either acutely or obtusely biased.
Take despression for example. It's easy for me to tell myself and everyone around me that I'm fine. It's just as easy to for everyone else to see through that bullshit and call me out for it. But that's the thing: all we do is call each other on our bullshit, think we're helping each other, and tauting that we're incredibly perceptive. Half the time, we're not even right in the moment, but the other person wants to confide in someone and thus makes it look like they're more perceptive than they actually are.
The problem is that some people pride themselves on their ability to "understand" how others work, and actively fluff their own ego when it comes to psychoanalyzing others, especially when they don't ask for it, want it, or need it.
I never try to pretend like I understand how people think or know why people do things. All I aim to do is come off as someone that cares. And yes, that is also largely a biased perception of myself. I won't even go as far as to say how accurate I feel it is of me regardless of how biased the self-evaluation it would be. It just really irks me when someone tries to tell me the person that I am, or why I'm acting a certain way: not because I still want to think that I know myself better than someone else, and at the very least, I will concede that we ourselves do know ourselves better than anyone else does.