So? If self is an illusion, and I was predetermined to be writing this post, does it really matter?
That depends what you mean by "does it matter"? Matter to what? If you're questioning whether there are any practical implications, then I'd say yes-- the ones I described before. It matters to me, for example, if a person has any actual control over their own actions or if their actions are entirely ruled by physics. If it's the former, then I feel justified to blame them for all, or at least some, of their actions. If the latter, I have no reason to. They are simply exhibiting a physical stimulus-response. I may then in turn respond to their stimulus-response by altering their stimulus to gain a more desirable response from them. Everything is stimulus-response. There is no need to attribute values of badness or goodness to the person themselves, though arguably there isn't one either way.
Based on the assumption that this is a deterministic universe:
I am a determinist because I had to be. I see all things as an inevitability because the physical variables have yielded that result. I take this into consideration when I employ my decision-making process, because I have to. This conversation, as you pointed out, had to happen exactly this way. To me, knowing, or thinking, that this is a deterministic universe grants a level of serenity, and contributes to sound judgment, that I would not be able to benefit from otherwise in some ways. In others, it does not. When that is the case, I act in the way I see best, knowing that that is the only thing I can do. Primarily, I forgive people of their mistakes (even if I don't show it) and I look for ways to alter their stimuli to get better responses in the future-- because I have to. This is the way the universe has made me, you might say.
I think it's silly to predicate the meaning of life on something so silly as "to be everything you possibly can be" or "to be the best person possible."
Well that's not at all what I was saying. What I was saying is that according to determinism, at least as I see it, you already are the best person you can possibly be. Everyone is. The universe is perfect, in a highly mathematical sense. All things are exactly as they should be, just as 2+2 should equal 4. That's the universe.
As for the value of living, that's determined by our ability to be happy, I think-- to be able to attribute values of goodness to things. We have the ability to say that life is good, and the biological imperative to choose a course that leads to happiness (based on the quality of our decision-making abilities), or perhaps more (or equally) accurately, the absence of things that we assign negative values to... namely: fear, anger, and sorrow.