I'm sorry for quoting myself, but the justification is that I just recently posted in the depression club something that has to do with exactly the same subject. Your question has been on my mind A LOT. It's the question which has hunted me, with varying frequency, for the last 3 years or so, though traceable back to my middle teens.
"An interesting line of thought: In recent months, I've began to think of the self, as Satre puts it, as a nothingness. Though not in his sense. By nothingness I only take that to mean that the self has no intrinsic properties apart from the ability to represent objects which is revealed (to consciousness/self/mind) with a certain phenomenological flavor /(ie. the represented coffee
tasting bitter, or the represented painting experienced as gloomy/, and to become aware of such representations (ie. representing yourself representing by way of an
intentional act a beer, a brown door, or yourself afflicted with pseudohypomania). Sometimes this nothingness predicates things of itself and, more often than not, it is believed. With time and new experiences, new predicates arise, and old ones are being disposed, forgotten, or changed into it's opposite. The set of predicates in immediate awareness (conscious, or crystalized in the post-conscious) is what you consider to be your self (you can say your self image). Altering, or removing these predicates changes the way in which you experience, how you act, and, subsequently, what you will achieve. If you remove all
possible predicates, perhaps you find out that there is something that can be truly 'said of' the self, with the result that there is no nothingness after all. But in most people, at least in me, there is a whole lot of nothingness! Accidental predicates that serve to fill in the void that is me, motivated by some principle that most likely is shared by us all."
Tbh. I think the only possible way that comes with any promise of reaching a somewhat accurate understanding of self is by routes such as the one lyra claimed to follow at one point. That is, by what can be referred to as personality experimentation. The reasoning being that if you want to understand what you are, you must find the unchangeable qualities of your self. The only way to know what is changeable, and what is not, is to strive towards changing what you, in your present moment, assume to be fundamental to your way of being. It isn't enough, here, to entertain an opposite to what you assume is (felt as a 'knowing'), but attempting to actually embody it. However, the road is difficult, and open only to those who have the courage and strong will necessary to attempt it because you can't change without everything else changing: your friends, your relation to family, your everyday.
An alternative might be to just seek out the extreme and radically different, and to do it often. But this, I think, is related to the former.
It might be that one discovers that it's (the self) only a process, but then one could attempt to understand
it as process.
This is all to say that I'm suspicious towards the claim that pure reasoning, a priori, is sufficient to reach an understanding of the self. I think you have to, as the scientists do, experiment, and to falsify and confirm. The obstacle that, for instance, the social sciences has in that it often confirms it's own hypothesis, applies in this case as well in that we are prone to confirm through experience our own hypothesis about ourselves.
Oh, and psychoactives temporarily changes the way you look at yourself and that around you. I think that it can be a highly helpful tool. It might make you confused, but the self is confusing. Being confused often just signals that you see a little bit more than you did before, that you are beginning to discover the further reach of it's complexity/richness/depth.