Why is there an unconscious?

This may seem like a strange question.  From the perspective of our personal experience, it's not clear why it shouldn't all just be conscious.  With a little training in introspection, I can succeed in making significantly more of that unconscious experience accessible to my consciousness, and this can be really useful.  So what's the point of having this hidden stuff to begin with?  You might answer that it conserves mental processing power, or something of the sort, and since this processing is evolutionarily expensive you want to use as little a possible.  However, it's not immediately clear why being conscious of running some mental algorithm should require more resources than just running the algorithm.  And anyway, this line of thought leads directly to a different version of the same problem.

You could equally well pose the question the opposite way around -- why is there consciousness at all?  This direction would probably make more sense from an evolutionary perspective.  What exactly does consciousness add to our ability to survive?  You might answer that it makes possible learning, or abstraction, or reason, or language.  But it's not clear that any of those things require consciousness.  Or perhaps it's not clear that consciousness is anything different from having those things?  Even if conscious computation doesn't turn out to require more resources, what's the point of having this curlicue added to the brain.  We sure make a big deal about it, but it's not obvious that it has any purpose.

If you put these two versions of the question together, you realize that an even better version is probably -- why is there a difference between the conscious and the unconscious?  A world with only one or the other wouldn't raise any issues.  But there's something mysterious about having both.  And isn't perhaps the oddest thing about this setup that they so often seem to be in opposition to one another?  Why are we fighting our selves?

I'm not sure I understand completely where this idea takes us, but I'd like to think our new understanding of repetition as process has something to contribute here.  We concluded that the process of repetition constructs identity.  In other words, repetition as a relation differs in kind from the identities of the things related and necessarily hides itself behind them.  Is this distinction exactly why there must be both a conscious and an unconscious?   The virtual needs the real and the real needs the virtual?  

Deleuze never seems to use the word "process" in D&R, despite the fact that one of his big influences, Whitehead, explicitly called his thinking a "process philosophy".  I'm not completely sure why Deleuze avoids the term.  Part of the explanation may be that it's all to easy to claim (as I have so many times already) that, "X is a process, not a thing" as if this just immediately elucidated something profound.  Have we really said anything important when we do that though?  Aren't we still using a concept of identity -- a process -- that just treats it like a more abstract thing?  Don't we push the concept around in our head like a little box, just like we would with anything else?  Perhaps Deleuze avoids using the term directly because the book itself is written as a definition of what a process is.  We have to discover what's important in the distinction between a process and a thing.  The movement, the displacement, the hiding, the lack of identity, the intersubjectivity.  A process necessarily happens in time.  But what is time?

We'll see in the next section that thinking about the virtual seems to culminate in in contemplating the difference in nature between problems or questions and their solutions.  The unconscious will be seen as a problem posing machine, a questioning machine.  These problems have a real 'objective' existence for Deleuze.  They aren't just a reflection of some fact that we don't happen to know right now.  They are, to use the jargon, ontological, and not epistemological problems.  While they may be objectively real in the colloquial sense, their reality is not of the same type as the solutions.  Solutions are real, but problems are virtual.  And questions are virtual objects.  Their being is ?-Being, (non)-Being, a non-Being that is not negation.

Being is also non-being, but non-being is not the being of the negative; rather, it is the being of the problematic, the being of problem and question.

Just in the place where I might expect a discussion of the unusual "being of a process", what makes a process distinct from a thing, we get instead a section on problems and their relationship to the unconscious.  It makes me think that the short but deep answer to our original question is: "because Time".